MCQs on Physical Science for Govt. Exams

• As the mass of the moon is 1/100 times the mass of Earth and the radius of the moon is ¼ times the radius of the Earth.
• As a result, the gravitational attraction on the moon is about 1/6th when compared to that of the Earth.

So, Moon has six times low gravity as compared to the gravity on Earth.

Weight on Earth = mg

Weight on Moon:

\({W_m} = \frac{1}{6}{W_E} = \frac{1}{6} \times m\times g= {mg\over6}\)

Mass of the body: Mass of the body is the measure of the amount of substance present in the body.

• The mass of the body is the same throughout the universe.

• A Sphygmomanometer is a device used to measure Blood Pressure.
• It consists of an inflatable cuff, a measuring unit, the mercury manometer, and a mechanism for inflation which may be manually operated bulb and valve or a pump electrically operated.
• It was invented in 1881 by Samuel Siegfried Karl Ritter Von Basch.

• Electric Current is measured by Ammeter.
• Wind speed is measured by Anemometer.
• Humidity is measured by Hygrometers.

• Resistance:
  • It measures the obstruction to current flow in an electrical circuit.
  • It is measured in ohms.
  • It is symbolized by the Greek letter omega (Ω).
  • It decreases with temperature in semiconductor because
    • Semiconductors do not have free electrons at normal temperature.
    • The electrons get free on heating and it behaves like conductors.
  • ​​It increases with temperature in the case of conductors.​

• ​Semiconductor:
  • It has the characteristics halfway between conductor and insulator.​
  • Its electrical properties make it suitable for use as the basis for computers and other electronic devices.
  • Its conductance is typically sensitive to changes in temperature, light, magnetic fields, and atom-level impurities.
  • Its constituent elements include silicon (Si), germanium (Ge), tin (Sn), selenium (Se), and tellurium (Te).

• Gamma rays have the shortest wavelength and highest frequency (energy) in the electromagnetic spectrum.
• They are electromagnetic waves with wavelengths in the range of 10^-12m and frequencies around 10²⁰- 10²⁴ Hz.
• They have a high penetrating power.
• They are a result of decaying radioactive material and can also be found in outer space.
• They are used in medical applications for sterilisation of equipment and cancer treatment.

• Other radiations in the Electromagnetic spectrum are:

• Reflection-
  • ​When the light rays fall on the plane surface it deviates from its path in the same medium.
  • or When a ray of light is incident on the plane surface is reflected back into the same medium it is termed as Reflection.
  • Example - Plane Mirror.
• A reflected ray: The ray of light that bounces back from the surface of reflection is called the reflected ray. All the rays of the incident, normal and reflected lie on the same plane.

• Coulomb’s Law talks about the magnitude of the attraction between the two charges.
  • It says that the force is directly proportional to the product of the quantity of the two charges.
  • F ∝ q1q2, where (F is Force, q1 and q2 are charges).
  • It is also inversely proportional to the square of the distance between them.
• i.e., F ∝ 1/r2 where (F is Force, r is the distance between the charges).
• Thus, the equation is
• \(F\; = \;k\frac{{{q_1}{q_2}}}{{{r_2}}}\;\)where k is the proportionality constant and is equal to 9 × 109 Nm2/C2.
• The Law was given by Charles-Augustin de Coulomb in the year 1784.

• Lenz's law states that the direction of the induced current in the coil will be always in such a way that it opposes the change which produces the current.
• According to Gauss law, the total electric flux linked with a closed surface called Gaussian surface is \(\frac{1}{ϵ_o}\) the charge enclosed by the closed surface.
• Ohm’s law states that at a constant temperature, the current through a conductor between two points is directly proportional to the voltage across the two points.

• There are 981 dynes in one gram weight.
• Dyne is a CGS unit.
• The weight of the mass of 1 gram of body is. w = mg.
  • w = 1gm×981cm/s2
  • w = 981 dyne.

• Newton and dyne are the units representing the force.
• So dyne is the unit of force in the centimeter-gram-second system of physical units
• 1 dyne equals = 0.00001 newtons
• 1 N = 10⁵ dyne

• Force:
  • Force is defined as the push or pull on an object with mass that causes it to change its velocity.
  • Force is an external agent capable of changing a body's state of rest or motion.
  • It has a magnitude and a direction.

CONCEPT

Viscosity: It is the property of a fluid, by virtue of which it opposes the relative motion between its different layers is known as viscosity.

This force is known as the viscous force.

Mathematically, \(F = - η A\frac{{dv}}{{dx}}\;\)

where, η = coefficient of viscosity, A = area, dv/dx = velocity gradient.

EXPLANATION

Fluid means any liquid or gas that can flow.

As described above,

• It opposes relative motion between adjacent layers therefore option 1 is correct.
• Viscosity is the property of fluid (liquid/gas) therefore, option 2 is incorrect.
• \(F = - η A\frac{{dv}}{{dx}}\; ⇒ η = - \frac{F}{A}\frac{{dx}}{{dv}} = \;P\frac{{dx}}{{dv}}\)
• η ∝ P ⇒ viscosity increases pressure increases and vice versa.

• Convex Mirror
  • A Convex Mirror curves outward like the back of a spoon.
  • In a convex mirror, light originating from the same point will reflect off the mirror surface and diverge.
  • Hence convex mirror is sometimes referred to as a diverging mirror.
  • The type of image formed by these mirrors is always imaginary or virtual.
• Uses of Convex Mirror
  1. It is used as a rearview mirror in the vehicle because it provides the maximum near field of view.
  2. In Sodium reflector lamp.

• Concave Mirror
  • A Concave mirror is a mirror that has a slightly inward curve like the inside of a spoon.
  • The Curved surfaces focus parallel rays from a great distance into a single point for enhanced intensity.
• Uses of Concave Mirror
  1. As a shaving glass
  2. As a reflector for headlights of vehicles, and searchlights.
  3. In Ophthalmoscope examines the eye, ear, and nose doctors.
  4. In Solar cookers.

Confusion Points

• Do not confuse between Concave/Convex Lens and Mirror
• Convex lens
  • The convex lens is also called a converging lens.
• Concave lens
  • The concave lens is also called a diverging lens.

• The formula for density is D = M/V [D=Density, M=Mass and V=Volume]
• Density is commonly expressed in units of grams per cubic centimetre.
  • It does not matter how large or small a sample of matter is, the same substance will always have the same density.
  • Because the ratio between the mass and volume remains the same.

• Mass is how much stuff something is made of.
• Volume is how much space an object takes up.
• Surface area is the measure of how much exposed area a solid object has.
• Specific gravity is also known as Relative density, is the ratio of the density of a substance to the density of given reference material.

• Water Equivalent:
  • It is defined as the mass of water which would absorb or evolve the same amount of heat as is done by the body in rising or falling through the same range of temperature.
  • It is the quantity of water whose thermal capacity is the same as the heat capacity of the body.
  • Its SI unit is Kilogram (Kg) and the dimensional formula is [M¹L⁰T⁰].
  • It is represented by W.
  • The product of the mass (m) of a substance by its specific heat equals numerically to the mass of water (W) that is equivalent in thermal capacity to the substance
    • ​W = mass x specific heat​

• ​A liquid in equilibrium with vapour has the same pressure and temperature throughout the system.
• Heat transfer always involves temperature difference between two systems or two parts of the same system.
  • Any energy transfer that does not involve temperature difference in some way is not heat.

• A fathometer is used to measure the depth of the ocean.
• The average depth of the ocean is about 12,100 feet.
• The deepest part of the ocean is called the Challenger Deep and is located beneath the western Pacific Ocean at the southern end of the Mariana Trench.

• The first depth measurements in the Mariana Trench were made by the British survey ship HMS Challenger, which was used by the Royal Navy in 1875 to conduct research in the trench.
• A fathometer is a depth finder that uses sound waves to determine the depth of water.

• God Particle spotted on 4-7-2012 is also called Higgs boson.
• Higgs boson is an elementary particle in the Standard Model of particle physics.
• It is produced by the quantum excitation of the Higgs field.
• Higgs's idea was that the universe is bathed in an invisible field similar to a magnetic field. Every particle feels this field—now known as the Higgs field.

• Noble prize in 2013 in physics had been given in the field of Universe.
• Two scientists had won the Nobel prize in physics for their work on the theory of the Higgs boson.
• Peter Higgs, from the UK, and Francois Englert from Belgium, had shared the prize.
• In the 1960s, they were among several physicists who proposed a mechanism to explain why the most basic building blocks of the Universe have mass.
• The mechanism predicts a particle - the Higgs boson - which was finally discovered in 2012 at the Large Hadron Collider (LHC) at Cern, in Switzerland.

• The energy that moving particles possess is Kinetic energy.
• Moving Water and Wind are good examples of Kinetic energy.
• Kinetic energy includes electrical, radiant thermal, and sound energy.​

• Magnetic Energy that energy is created by the strength of the magnetic field.
• Electrical energy is that energy where's movement of electrically positive charged particles.
• Potential energy is a kind of energy stored in objects.

• The Colour of the soap bubble is due to the interference of reflected light from the film-air interface.

• In the case of soap bubble made of a transparent soap film with plane parallel faces separated by a distance t as shown in the figure below.

• Suppose a parallel beam of light is incident on the film at an angle i. The wave is divided into two parts at the upper surface, one is reflected and the other is refracted.
• The refracted part enters into two parts; one is transmitted out of the film and the other is reflected back.
• Multiple reflections and refraction take place and a number of reflected waves, as well as transmitted waves, are sent by the film.

• The interference of reflected light waves in the thin film results in the formation of either Constructive or Destructive.

• Scattering: The intensity of scattered light is inversely proportional to the fourth power of the wavelength; provided the scatter is smaller in size than the wavelength of light
• Dispersion: The white light gets split into constituent "VIBGYOR".
• Diffraction: It is spreading out of any wave due to an encounter with any obstacle.

• Coronagraph:
  • A coronagraph is a specialized instrument designed to block out the light of the sun so that researchers can glimpse the burning star's hot, thin, outermost layer, called the corona.
  • A French astronomer Bernard Lyot invented the coronagraph in the 1930s, according to the American Museum of Natural History, and the instrument has since found many other uses.
  • The sun's corona is normally visible only during solar eclipses when the moon's shadow covers the bright central layers of our parent star and allows its dimmer corona to appear.
  • A coronagraph mimics this natural phenomenon with a circular mask that sits inside a telescope and selectively blocks the bulk of the sun's light.

• The heat transfer, in case of liquids and gases. takes place according to Convection.
• Convection is the process by which heat is transfer from one place to another in a medium by the movement of particles of the medium. Convection occurs in fluids (liquid and gases).

• The recoil in a gun is caused due to the forward momentum of the bullet.
  • The force with which the bullet is fired is balanced by the recoil of the gun.
  • The gunman gets a jerk on firing a bullet from his gun.
  • This is because when a bullet is fired from a gun, the force sending the bullet forward is equal to the force sending the gun backwards but due to the high mass of the gun, it moves only a little distance backwards giving a jerk to the gunman.
  • So, the recoil follows Newton's third law of motion.

Confusion Points

• The launching of rockets is based on the principle of the law of conservation of momentum, while the recoil of the gun is an example of Newton's third law of motion i.e. momentum.

• A marathon runner is not able to stop himself right after crossing the finish line.
  • He/she tends to take time and cover a few meters of distance running beyond the finish line.
  • This is because the inertia of motion or Newton's first law of motion resists a sudden termination of motion and compels the body to maintain its state of motion.
• For a rocket to leave the earth's orbit and enter outer space, a force called thrust is required.
  • As per the second law of motion given by Sir Issac Newton, the force is proportional to the acceleration, therefore, to launch a rocket, the magnitude of thrust is increased, which in turn increases the acceleration.
  • The speed achieved by the rocket finally helps it to escape the earth's gravitational field and enter space.
• In simple terms, Newton's second law of motion states that if force is applied to any object that has mass, it will result in the production of an equivalent amount of acceleration in the object.
  • For instance, when we turn on the ignition system of the car, the engine of the car produces a sufficient force that enables the car to move with proportionate acceleration.

• Electromagnetic Force
  • It is a fundamental force in nature which acts between charged particles and is a combination of all electrical and magnetic forces.
  • The electromagnetic force can be attractive or repulsive in nature.
• The four Fundamental forces of nature
  1. Gravitational Force
  2. Weak Nuclear Force
  3. Electromagnetic Force
  4. Strong Nuclear Force

• Torque force or opening/closing force is the force required to open/close a bottle or other containers with a screw cap.
• Torque is the measure of the force that can cause an object to rotate about an axis.
• Torque can be defined as the rotational equivalent of linear force.
• The point where the object rotates is called the axis of rotation. In physics, torque is simply the tendency of a force to turn or twist.
• The unit of torque is Newton–meter (N-m).
• Applications of Torque:
  • Seesaws and Wrenches
  • Gyroscopes
  • A pendulum or a parachute is applying torque when swinging
  • A person riding a bicycle
  • Flag flying on a mast

• Paramagnetic substances:
  • They get weakly magnetized when placed in an external magnetic field.
  • They tend to move from a region of a weak magnetic field to a strong magnetic field.
  • They get weakly attracted to a magnet.
  • Their atoms (or ions or molecules) possess a permanent magnetic dipole moment of their own.
  • They include substances like aluminium, sodium, calcium, oxygen (at STP) and copper chloride, etc.​

• Curie’s law
  • It states that the magnetization of a paramagnetic material is inversely proportional to the absolute temperature.
  • When the field is increased or the temperature is lowered, the magnetization increases until it reaches the saturation value
    at which all the dipoles are perfectly aligned with the field.

• Acceleration is the rate of change of the velocity of an object with respect to time.
• Acceleration is a vector quantity (has magnitude and direction both).
• The unit of acceleration is meter per second square(m/s²) or LT^-2.

• The speed of an object is the magnitude of the rate of change of its position with time, it is thus a scalar quantity.
  • Unit of speed is meter per second (m/s) or LT^-1.
• A displacement is a vector whose length is the shortest distance from the initial to the final position of a point undergoing motion.
  • Unit of displacement is meter (m).
• The velocity of an object is the rate of change of its position with respect to a frame of reference and is a function of time.
• Velocity is equivalent to a specification of an object's speed and direction of motion.
• It is a vector quantity.
  • Unit of velocity is meter per second (m/s) or LT^-1.

• Calories and joule both are the units to measure the energy.
• Scientists define energy as the ability to do work.
• Modern civilization is possible because people have learned how to change energy from one form to another and then use it to do work.
• People use energy to walk and bicycle, move cars along roads and boats through water, cook food on stoves, make ice in freezers, light our homes and offices, manufacture products, and send astronauts into space.
• There are many different forms of energy, including Heat, Light, Motion, Electrical, Chemical, Gravitational etc.

• 'Force’ divided by ‘mass’ is equal to acceleration.

Explanation:

• Newton's second law is often stated as F = ma, which means the force (F) acting on an object is equal to the mass (m) of the object times its acceleration (a). This means the more mass an object has, the more force you need to accelerate it, and the greater the force, the greater the object's acceleration.
  • Force(F) = Mass(m) × Acceleration(a).
• Unit of Force = SI unit of Force is in Newtons (N).
• 1 Newton is equal to 1 kg*m*s-2.
• The acceleration of an object is directly related to the net force and inversely related to its mass.
• The acceleration of an object depends on two things, force and mass.
• Mass is a measure of the amount of matter in an object.
• Mass is usually measured in grams (g) or kilograms (kg).
• An object's mass is constant in all circumstances, contrast this with its weight, a force that depends on gravity.

• The atmospheric refraction is responsible for the twinkling of stars.
• As the light from the stars enters the earth's atmosphere it suffers refraction and causes the twinkling of light.

• Refraction- When a light ray travels from one transparent medium to another transparent medium then it deviates from its original path and this phenomenon is called Refraction.
  • For example- when light travels from the Rarer medium (Air) to the Denser medium (Water) is deviates towards the Normal.
• Laws of refraction
  • The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant.
  • The Normal, Incident ray, Refracted ray lie on the same plane at the point of Incidence.

• Diffraction- The bending of a light ray from its path after striking an obstacle.
  • Diffraction is the result of interference.
• Dispersion- The separation of visible light into its different colours is known as dispersion, Example- Prism( splitting of white light into seven colours).
• Scattering - It is the Phenomenon in which light gets deviated from its straight path after striking the obstacle like dust or gas molecules, water vapour, etc.

• The upward buoyant force that is applied to a body submerged in a fluid, whether wholly or partially, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the centre of mass of the displaced fluid, according to Archimedes' principle.
• The Archimedes law, which was developed by Archimedes of Syracuse in Greece, provides the thrust force value.
• When an object is submerged in a liquid, whether completely or partially, the apparent weight loss is equal to the weight of the liquid that it has displaced.

• According to Bernoulli's principle, the total mechanical energy of a moving fluid, which includes the kinetic energy of the fluid's motion as well as the gravitational potential energy of elevation and pressure, remains constant.
• According to the Beer-Lambert law, there is a linear relationship between a solution's concentration and absorbance, making it possible to determine a solution's concentration by observing its absorbance.
• According to Blaise Pascal's law, a pressure change in a confined, incompressible fluid that happens at any place is distributed evenly throughout the fluid, causing the identical change to occur everywhere.

Concept:

The apparent weight of a person inside a lift

• When the lift moves upward with acceleration a. Then the net upward force on the person is-

R - mg = ma

∴ Apparent weight, R = mg + ma = m (g + a)

So, when a lift accelerates upwards, the apparent weight of the person inside it increases.

• When the lift moves downwards with acceleration a. Then the net downward force on the person is-

Mg - R = ma

∴ Apparent weight, R = mg - ma = m (g - a)

So, when a lift accelerates downwards, the apparent weight of the person inside it decreases.

• When the lift is at rest or moving with uniform velocity v downward/upward. The acceleration a = 0, then the net force on the person is-

R - mg = m x 0 = 0

R = mg

∴ Apparent weight = Actual weight

• When the lift falls freely. If the supporting cable of the lift breaks, the lift falls freely under gravity. Then a = g. The net downward force on the person is -

R = m(g - g) = 0.

• Thus, the apparent weight of the man becomes zero. This is because both the man and the lift are moving downwards with same acceleration ‘g’ and so there are no forces of action and reaction between the person and the lift. Hence a person develops a feeling of weightlessness when he falls freely under gravity.
• Newton's second law states that the acceleration of an object is directly related to the net force and inversely related to its mass.
  • The acceleration of an object depends on two things, force and mass.

F = ma

Where F = force acting on body, m = mass of body, a = acceleration.

Calculation:

Given: mass = m, a = 2g N = ?

According to Newtons 2nd law of motion,

ΣF = Ma

N - Mg = 3Mg

N = 4 Mg

Reaction on the floor by the man is 4 mg and vertically upward in direction.

• The SI unit of acceleration is meters/second² (m/s²).
• Hence, the power of the second is -2 as it is in the denominator.
• Acceleration (a) is defined as the rate of change in velocity.
• Velocity is a vector quantity, and therefore acceleration is also a vector quantity.

• Types of acceleration
• Uniform acceleration
  • When an object is travelling in a straight line with an increase in velocity at equal intervals of time, then the object is said to be in uniform acceleration. The free-falling of an object is an example of uniform acceleration.
• Non-uniform acceleration
  • When an object is travelling with an increase in velocity but not at equal intervals of time is known as non-uniform acceleration. Bus moving or leaving from the bus stop is an example of non-uniform acceleration.
• Instantaneous acceleration
  • The acceleration of an object at any instant of time is known as instantaneous acceleration.

• A convex mirror is a mirror whose reflecting surface is away from the centre of the curvature.
• A convex mirror is also known as a diverging mirror.

• When the object is placed at the infinity of the convex mirror, then the image is formed at the focus, behind the mirror and the nature of the image is erect, virtual, and highly diminished.
• The image formed by the convex mirror is always erect, virtual, and smaller in size (diminished).
• When the object is placed in between the infinity and pole of the convex mirror, then the image is formed between the focus and the pole, behind the mirror.

• Nature Position and relative size of the image formed by a convex mirror.

• As Current, I = 1 A
• time, t = 1 minute = 1 × 60 = 60 seconds
• let the total charge flown = Q
• We know that Q = I × t
• Where Q = charge in Coulombs
• I = Current flowing in Ampere
• t = time duration in seconds
• So now Q = 1 × 60
• Q = 60 A sec or Coulombs
• The resistance given here is Irrelevant

• Rectilinear motion is also known as Linear motion.
• Rectilinear motion is one-dimensional motion along a straight line, and can therefore be described mathematically using only one spatial dimension.
• A linear motion in which the direction of the velocity remains constant and the path is a straight line.
• Gravitational forces acting on objects resulting in free fall is an example of rectilinear motion.
• Kids sliding down from a slide is a rectilinear motion.
• The motion of planes in the sky is a rectilinear motion.

• Periodic motion is a motion repeated in equal intervals of time.
• Periodic motion is performed, for example, by a rocking chair, a bouncing ball, a vibrating tuning fork, a swing in motion, the Earth in its orbit around the Sun, and a water wave.
• Rotational motion can be defined as the motion of an object around a circular path, in a fixed orbit.
• A motion repeating itself is referred to as periodic or oscillatory motion.
• An object in such motion oscillates about an equilibrium position due to a restoring force or torque.

• The opposing forces that are experienced by objects when moving against each other are termed as friction.
• Static friction, sliding friction, and rolling friction are the resistances experienced by stationary, moving, and rolling objects respectively.
• During sliding, contact points do not get enough time to get interlocked properly. Therefore, less friction.
  • But, when the object is at rest, the surfaces interlock well, therefore friction is more. Due to this sliding friction is less than static friction. Hence, Statement 2 is correct.
• The force of friction that appears between two sliding surfaces which are in contact is called sliding friction. The area of contact is less in the case of rolling than in the case of sliding, therefore rolling friction is less than the sliding friction. Hence, Statement 1 is also correct.
• Rolling friction is the resistance to motion experienced by a body when it rolls upon another. It is much less than sliding friction for the same pair of bodies.

• Static friction keeps an object stationary, so it is the maximum.
• Rolling friction, on the other hand, provides the least resistance as the contact time and contact area between the two surfaces is the least.
• Therefore, static friction is the strongest form of frictional force followed by sliding friction which is weaker than static but stronger than rolling friction.

• The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of the Dobson Unit (DU).
• Dobson Unit (DU) is defined to be 0.01mm thickness at STP - (zero degrees Celcius and 1 atm press), A slab of 3mm corresponds to 300 DU.
• Ozone forms a layer in the stratosphere, thinnest in the tropics (around the equator) and denser towards the poles.​

• A carat is a unit of weight used to measure the size of a gemstone such as a diamond. A karat is a measurement indicating the proportion of gold in an alloy out of 24 parts, so 18K gold is 18/24 parts gold. However, the use of carat (in place of karat) to indicate the fineness of gold is also considered acceptable.
• A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for accurate measurement of components in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier, and digital calipers.

• The Ozone layer is the layer in Earth's atmosphere which contains a relatively high concentration of ozone (O₃). This layer absorbs 97-99% of the sun's high-frequency ultraviolet light, which is potentially damaging to life on earth.

• Radio waves
  • In the electromagnetic spectrum, radio waves have wavelengths that are longer than those of infrared light.
  • They have wavelengths that range from 1 millimetre to 100 kilometres, and frequencies that range from 300 GHz to as low as 3 kHz.
  • Radio waves move at the speed of light, just like all other electromagnetic waves.
  • Lightning and celestial objects are the two main sources of naturally produced radio waves.
  • Fixed and mobile radio communication, broadcasting, radar, and other navigation systems, communications satellites, computer networks, and countless more applications all require artificially produced radio waves.
  • In the Earth's atmosphere, different radio wave frequencies propagate in different ways.
  • Shorter waves can travel around the world and reflect off the ionosphere, while much shorter wavelengths bend or reflect very little and move along a line of sight.
  • Long waves may cover a portion of the Earth quite consistently.

• A rectifier is an electrical device that converts alternating current to direct current which flows only in one direction.​
• A rectifier is a device that converts an alternating current into a direct current.
• A p-n junction can be used as a rectifier because it permits current in one direction only.

• An electrical device that is used to transfer electrical energy from one electrical circuit to another is called a transformer.
• An ammeter is an instrument that is used to measure the current flowing through the circuit.
• A voltmeter is used to measure the electric potential difference between two points in a circuit.

• “An object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force”. Above stated law is First law of motion.

• The first law of motion:
  • Newton's first law of motion is known as the Law of Inertia.
  • Newton's first law states that if a body is at rest or moving at a constant speed in a straight line.
    • it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force.
  • There are two conditions on which the 1st law of motion is dependent:
    • Objects at rest :
      • ​ When an object is at rest velocity (v= 0) and acceleration (a = 0) are zero.
      • Therefore, the object continues to be at rest.
    • Objects in motion :
      • When an object is in motion, velocity is not equal to zero (v ≠ 0) while acceleration (a = 0) is equal to zero.
      • Therefore, the object will continue to be in motion with constant velocity and in the same direction.​
  • Newton’s First Law of Motion Examples in Daily Life:
    • Wearing a seat belt in a car while driving is an example of Newton’s 1st law of motion.
      • If an accident occurs, or if brakes are applied to the car suddenly, the body will tend to continue its inertia and move forward, probably proving fatal.
      • To prevent such accidents seat belts are used which stops your body from moving forward in inertia avoiding danger.

• Newton's Third Law of Motion states that 'To every action, there is an equal and opposite reaction'.
• Newton's Second Law of motion states that the rate of change of momentum of an object is proportional to the applied force in the direction of the force. i.e. F=ma. Where F is the force applied, m is the mass of the body, and a is the acceleration produced.

• The technology of production of ultra-high magnetic fields is based on Superconductivity.
  • Superconductivity is the ability of certain materials at very low temperatures to conduct electric current with practically zero resistance.
• The superconductor exhibits zero electrical resistance below the transition temperature.
  • The temperature at which the metals change from a normal conducting state to a superconducting state is called critical temperature/transition temperature.
• An example of superconductors is mercury.
  • It becomes a superconductor at 4 K
• The modern theory of superconductivity was put forward by Bardeen, Cooper, and Schrieffer in 1957.

• Photoelectric Effect
  • It is a phenomenon where electrons are ejected from a metal surface when the light of sufficient frequency is incident on it.
  • The photoelectric effect was discovered by Heinrich Rudolf Hertz.
  • Einstein later suggested that light behaved like a particle and that each particle of light had energy called the photon.
  • Einstein received the Nobel Prize in Physics in 1921 for discovering the law of the photoelectric effect.

• In the motion of lift from an airfoil, the air is deflected downwards by the airfoil’s action, and in reaction, the wing is pushed upward. This shows Newton 3rd Law

• In the motion of lift from an airfoil, the air is deflected downwards by the airfoil’s action, and in reaction, the wing is pushed upward.
  • An airfoil generates lift by exerting a downward force on the air as it flows past.
• According to Newton's third law, the air must exert an equal and opposite (upward) force on the airfoil, which is lifted.
• The airflow changes direction as it passes the airfoil and follows a path that is curved downward.
• Newton's Third Law of Motion states that 'To every action, there is an equal and opposite reaction'.

• A fielder pulling his hand back while catching a ball is an application of Newton's second law of motion.
  • Newton's Second Law of motion states that the rate of change of momentum of an object is proportional to the applied force in the direction of the force. i.e. F=ma. Where F is the force applied, m is the mass of the body, and a is the acceleration produced.
• When a bus starts suddenly, the passengers receive a backward jerk an application of Newton's first law of motion.
  • Newton First law states that Every object remains in uniform motion in a straight line unless compelled to change its state by the action of an external force.
• When we stop pedalling, the bicycle slows down due to the frictional force acting on the bicycle.

• Radio Waves:
  • They have the longest wavelengths in the electromagnetic spectrum.
  • Their wavelengths range from 1 millimetre to 100 kilometres.
  • They are produced by the accelerated motion of charges in conducting wires.
  • Their concept was first predicted by James Maxwell and later demonstrated by Heinrich Hertz.
  • Cellular phones communicate by transmitting radio waves through a network of fixed antennas called base stations.
    • ​When we talk on a cellular phone, it acts as a transmitter and our voice is carried on radio waves to the person we are calling.
    • Another person's phone acts as the receiver and converts the signal back into our voice.

• Microwaves:
  • They are short-wavelength radio waves.
  • Their frequencies lie in the gigahertz (GHz) range.
  • Due to their short wavelengths, they are suitable for the radar systems used in aircraft navigation.
• ​Gamma Rays:
  • They lie in the upper-frequency range of the electromagnetic spectrum.
  • They have wavelengths of about 10^-10m to less than 10^-14m.
  • They are used in medicine to destroy cancer cells.

• Net charge 'Q' flows across any cross-section of a conductor in time 't', then the current 'I' is \(\frac{Q}{t}\)
• The flow of charge in a definite direction is called an electric current.
• \( I =\frac{ne}{t}\)
• Where e = 1.6 x 10^-19 C.
• so for making a charge of one Coulomb, the number of electrons required will be:
  n = 1/(1.6*10^-19)
• 1 coulomb of charge = 6.25 x 1018 electrons.

• A simple pendulum consists of a small metallic ball or a piece of stone suspended from a rigid stand by a thread. The metallic ball is called the bob of the pendulum.

• A point mass attached to a light inextensible string and suspended from fixed support is called a simple pendulum.
• The vertical line passing through the fixed support is the mean position of a simple pendulum.
• The vertical distance between the point of suspension and the centre of mass of the suspended body (when it is in the mean position) is called the length of the simple pendulum denoted by L.
• A simple pendulum is a mechanical arrangement that demonstrates periodic motion.
• The simple pendulum comprises a small bob of mass ‘m’ suspended by a thin string secured to a platform at its upper end of length L.

• The three parts of a pendulum are
  • cable or wire
  • bob or weight,
  • fixed point
• The fixed point is the starting point of where the wire hangs from and the weight is what's attached to the wire or the endpoint of the wire.
• Depending on the length of the wire, the pendulum moves at a certain uniform speed.
• A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them.
• a round handle, or a small, round device for controlling a machine or electrical equipment.
• A brass doorknob turns/Twiddle the little knob to adjust the volume.

• Sonar is a technique that uses sound propagation to navigate, measure distances, and communicate with or detect objects on or under the surface of the water, such as other vessels.
• SONAR stands for "Sound Navigation and Ranging".
• Sound waves emitted by or reflected from the object are detected by sonar apparatus and analyzed for the information they contain.
• Scientists primarily use sonar to develop nautical charts, locate underwater hazards to navigation, search for and map objects on the seafloor such as shipwrecks, and map the seafloor itself. There are two types of sonar—active and passive.

• Surface gravity varies inversely with the square of the planet's radius.
• So doubling the radius would reduce gravity by a factor of four.
• Hence the gravitational force exerted on the earth by the sun would be one-fourth of what it is now.

• Gravitational force:
  • The gravitational force is a force that attracts any two objects with mass.
  • The force of attraction between any two bodies is directly proportional to the product of their masses and is inversely proportional to the square of the distance between them.
  • Gravitational force Formula:
  • \(F = {G.m1.m2\over r^2}\)

• The acceleration of an object is said to be uniform when an object travels in a straight line and its velocity increases or decreases by equal amounts in equal intervals of time.
• A body is said to have a uniform acceleration when it travels in a straight line with its velocity increasing at equal intervals of time.
  • For uniform acceleration, the displacement- time graph is a parabola of a symmetric displacement axis.
• An object is said to be with nonuniform acceleration if the velocity of the object changes by unequal amounts in equal intervals of time.
  • Velocity-time graph for the Non-uniform acceleration is a curved line.

• Acceleration: The rate of change of velocity is called the acceleration of the body. i.e.,

\(a = \frac{{{v_2} - {v_1}}}{{{t_2} - {t_1}}}\)

• Where v2 = velocity of the object at t2 and v1 = velocity of the object at t1
• It is a vector quantity.
• Its direction is the same as that of change in velocity (Not of the velocity).

• Seismic waves:
  • Seismic waves or vibrations originate from the focus and are propagated in all directions.
  • These vibrations travel through the rocks in the form of elastic waves.
  • Mainly three types of waves called P wave, S wave, and L wave.
• L waves:
  • These are called long waves or surface waves.
  • These are the slowest among the seismic waves and most destructive.
  • Therefore these are the last to be recorded.
  • They travel at the rate of 4-5v km/sec.
  • These waves are capable of traveling through solids and liquids.
  • The destruction at the time of the earthquake is caused by these waves only.
  • These waves do not travel towards the interior of the earth from the focus.
  • They are of 2 types - Rayleights and Love waves.
• P waves:
  • These are primary waves (longitudinal or pressure waves). These are the fastest among the seismic waves.
  • They travel as fast as 8-13 km/sec depending upon the density and elasticity of the medium.
  • Therefore, when an earthquake occurs, these are the first wave to reach any seismic station and hence the first to be recorded.
  • These waves are capable of travelling through solids, liquids and gases.
• S waves:
  • These are called shear waves, transverse waves. As compared to P waves these are relatively slow.
  • They travel at the rate of 5-7 km/sec. These waves are capable of travelling only through solid.

• First law of motion can explained as 'An object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force.'
• The first law of newton implies that things cannot stop, start or change direction all by themselves.
• The things require some outside force.
• This property to resist changes of massive bodies in their state of motion is called inertia.

• The Second Law of newton states that the force acting on the body is equal to the product of its acceleration and mass.
• The Third Law of Newton states that for every action there is an opposite and equal reaction.
• The first law of thermodynamics only gives information about the energy balance when a system undergoes a change of state.
  • But it does not help to predict whether the change of state is feasible or not.

Concept:

• ​According to the Gaussian lens equation,
  • \(\frac{1}{f} =\frac{1}{v} - \frac{1}{u}\)
  • where,
    • v= Distance between the image and optical center of the lens,
    • u =Distance between object and optical center of the lens

    • f = focal length

Calculation:

From the given data,

v = 60m

u = - 20m

f =?

By applying the Gaussian lens formula,
\(\frac{1}{f} =\frac{1}{v} - \frac{1}{u}\)

\(\frac{1}{f} =\frac{1}{60} - \frac{1}{- 20}\)
\(\frac{1}{f} =\frac{1}{60} +\frac{1}{20}\)

\(\frac{1}{f} =\frac{1}{15}\)

Which gives f = 15 m

Hence, 15 m is the correct answer.

• The power of a lens is reciprocal to its focal length.
  • ie. Power of lens = \(1\over f\)
  • SI Unit of power of lens is Dioptre.

• Acceleration is the name we give to any process where the velocity changes.
• If the acceleration is negative, then the object is slowing down, and if the acceleration is positive, then the object is speeding up.
• Newton's second law states that Force(F) applied to a body is the product of its mass(m) and acceleration(a).

​​CALCULATION:

• Given,
  • F= 10N, m = 250 gm, a= ?
• using the formula \(\displaystyle F=m*a\) and substituting the values

10 = 0.25 x a (∵1 kg=1000 gm)

a = 10/0.25

= 40 m/s²

Hence, the acceleration of the ball is 40 m/s².

• Newton's second law is a quantitative description of the changes that a force can produce in the motion of a body.
• Newton's second law states that the time rate of change of the momentum of a body is equal in both magnitude and direction to the force imposed on it.
• A force applied to a body can change the magnitude of the momentum or its direction or both.

• An anemometer is an instrument that measures wind speed and wind pressure. Anemometers are important tools for meteorologists, who study weather patterns.
• A sling psychrometer can be used to determine the humidity of the surrounding air because its wet bulb temperature is nearly the same as the adiabatic saturation temperature.
• The standard instrument for the measurement of rainfall is the 203mm (8 inches) rain gauge. This is essentially a circular funnel with a diameter of 203mm which collects the rain into a graduated and calibrated cylinder.
• A hygrometer is an instrument used to measure the amount of water vapour in the air, in soil, or in confined spaces.

• In 1662, Christopher Wren created the first tipping-bucket rain gauge in Britain in collaboration with Robert Hooke.​

• LED in electronics refers to Light Emitting Diode.
• It is a semiconductor electronic component that converts electrical energy into light energy.

• LED works on the principle of quantum levels in an atom, where the electron releases energy when it moves from lower energy level to higher energy levels.
• This release of energy is the LED is in the form of photons that give light.
• Gallium is the major element used in its production.
• Various element combinations with Gallium and input voltages give rise to various colours.
• It is mostly used in the display devices which we use regularly.