Physics MCQ Quiz - Objective Question with Answer for Physics - Download Free PDF

The correct answer is the Microwave.

Key Points

• A microwave oven uses microwaves to heat food.
• In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz).
• Radio waves in this frequency range absorbed by water, fats, and sugars. When they are absorbed they are converted directly into atomic motion or vibration.
• Therefore heavy motion or vibration is converted into heat.

Important Points

• Microwaves are not absorbed by most plastics, glass, or ceramics.
• The frequency of the Microwave equals the resonance frequency of water. Therefore foods could be heated up by the oscillation of water molecules.

Additional Information

• An Electric heater, Electric blub (with filament), Electric iron is the electrical device that converts an electric current into heat.
• They working on the principle of the Joule heating effect.
  • An electric current passing through a resistor will convert that electrical energy into heat energy.

The correct answer is Newton's first law.

Key Points

• Newton's laws of motion-
  • ​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 force.
    • This postulate is known as the law of inertia. The law of inertia was first formulated by Galileo Galilei for horizontal motion on Earth and was later generalized by René Descartes.
    • Before Galileo, it had been thought that all horizontal motion required a direct cause. Still, Galileo deduced from his experiments that a body in motion would remain in motion unless a force (such as friction) caused it to come to rest.
  • Newton’s second law is a quantitative description of the changes that a force can produce in a body's motion.
    • It states that the time rate of change of a body's momentum is equal in both magnitude and direction to the force imposed on it.
    • The momentum of a body is equal to the product of its mass and its velocity. Momentum, like velocity, is a vector quantity, having both magnitude and direction.
    • A force applied to a body can change the magnitude of the momentum, direction, or both.
    • For a body whose mass m is constant, it can be written in F = ma, where F (force) and an (acceleration) are vector quantities.
    • If a body has a net force acting on it, it is accelerated by the equation. Conversely, if a body is not accelerated, there is no net force acting on it.
  • Newton’s third law states that when two bodies interact, they apply forces to one another that are equal in magnitude and opposite in direction.
  • The third law is also known as the law of action and reaction. This law is important in analyzing static equilibrium problems, where all forces are balanced, but it also applies to bodies in uniform or accelerated motion.
  • The forces it describes are real ones, not mere bookkeeping devices. For example, a book resting on a table applies a downward force equal to its weight on the table.
  • According to the third law, the table applies an equal and opposite force to the book. This force occurs because the book's weight causes the table to deform slightly so that it pushes back on the book like a coiled spring.

Explanation:

• Dispersion is the phenomenon by which white light splits into its 7 constituent colours while moving from one transparent medium to another.
• The 7 colours are red, orange, yellow, green, blue, indigo and violet.
• Rainbow is formed due to the dispersion of sunlight as it passes through droplets of water in the air.
•  A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms.
• They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop.
• Due to the dispersion of light and internal reflection, different colours reach the observer’s eye.

Additional Information
Reflection 

• The phenomena in which light ray is sent back into the same medium from which it is coming, on interaction with boundary, is called reflection.
• Laws of reflection: it states that, if a light ray is reflected from a plane flat polished surface its angle of the incident will always be equal the angle of reflection

 i.e., The angle of incidence (θ i ) = Angle of reflection (θ r )

Refraction

• The bending of a ray of light when it goes from one medium to another is called refraction of light.
  • When light enters from a rarer to a denser medium it bends towards the normal to the interface of the media.
  • Similarly, when light travels from a denser to the rarer medium it bends away from the normal.
• In refraction through a glass slab, the ray that first falls on the slab is incident ray, when it enters the slab it is called refracted ray and the outcoming ray is called an emergent ray.

The following diagrams shows the refraction of light through a glass slab:

• Applying the above-given principles it can be observed that emergent ray is parallel to the incident ray (here, AE is parallel to CD). 

Diffusion:

• When the light rays are reflected from a piece of paper and the reflected beam is scattered. Then this phenomenon is called diffusion of light.

Concept:

• A sound is a form of energy that produces the sensation of hearing in our ears.
• Sound is a type of longitudinal wave.
• Sound is measured in Decibels(Db).
• The speed of the sound varies in different mediums.

Explanation:

• Sound from a violin and a flute played at the same time travel at the same speed.
  • Both the sounds travel through the same medium which is air.
  • Both the sound travel through at the same speed at the same time but the sound we receive are different due to characteristics associated with the sound such as pitch and amplitude.
  • Hence, option 1 is correct.
• Two sound waves of the same intensity would not be perceived to have the same loudness because of the human's ear tendency to amplify sounds having frequencies in the range from 10kHz to 50kHz, sounds with these intensities seem louder to the human ear. Hence, option 2 is incorrect.
• Speed of sound in hot air is more than that of the room temperature because heat makes air molecules move around faster. Hence, option 3 is correct.
• The speed of sound depends on the density of the material.
  • Tightly packed material molecules transfer the sound at high speed.
  • Speed of sound is fastest in Solids, Liquids then Gas.
  • Hence, option 4 is correct.

Thus, the incorrect statement is that two sound waves of the same intensity will always have equal loudness. 

Important Points Amplitude:

• Amplitude is the measure of compression or rarefaction of particles of a medium through which sound is traveling.
• The higher the amplitude, the louder the sound.
• The amplitude A is related to loudness as loudness ∝ A2

Frequency:

• Frequency refers to the rate of vibration of sound.
• The pitch of a sound is decided by the measure of frequency.
• The higher the frequency, the shriller the sound.
• Frequency measured in Hertz (Hz).

Additional Information Sound in the air: 

• In a gas-like air, the particles are generally far apart so they travel further before they bump into one another.
• There is not much resistance to movement so it doesn’t take much to start a wave, but it won’t travel as fast.

Sound in water:

•  In water, the particles are much closer together, and they can quickly transmit vibrational energy from one particle to the next.
• This means that the sound wave travels over four times faster than it would in the air, but it takes a lot of energy to start the vibration.

Sound in solids: 

• In a solid, the particles are even closer together and linked by chemical bonds so the wave travels even faster than it does in either liquid or air, but you need quite a lot of energy to start the wave at the beginning.

Concept:

• Sound: A sound is a form of energy that produces the sensation of hearing in our ears.

Amplitude:

• Amplitude is the measure of compression or rarefaction of particles of a medium through which sound is traveling.
• The higher the amplitude, the louder the sound.
• The amplitude A is related to loudness as loudness ∝ A2

Frequency:

• Frequency refers to the rate of vibration of sound.
• The pitch of a sound is decided by the measure of frequency.
• The higher the frequency, the shriller the sound.
• Frequency measured in Hertz (Hz).

Explanation:

• The loudness and softness of a sound wave is the sensation that depends upon its amplitude.
•  Since the loudness depends on amplitude. So, to change a feeble sound to a loud sound students should increase the amplitude of the sound because the large amplitude produces a loud sound whereas the small amplitude produces a feeble sound.

Therefore, the correct answer is the amplitude of the sound.

CONCEPT:

• Wave: The disturbance that transfers energy from one place to another is called a wave.

There are mainly two types of waves:

1. Transverse waves: The wave in which the movement of the particles is at right angles to the motion of the energy is called a transverse wave. Light is an example of a transverse wave.
2. Longitudinal wave: The wave in which the movement of the particles is parallel to the motion of the energy is called a longitudinal wave. The sound wave is an example of a longitudinal wave.

EXPLANATION:

• Light-wave is a transverse wave because its components vibrate perpendicular to its direction of propagation. So option 1 is correct.

The correct answer is Newton's first law.

Key Points

• Newton's laws of motion-
  • ​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 force.
    • This postulate is known as the law of inertia. The law of inertia was first formulated by Galileo Galilei for horizontal motion on Earth and was later generalized by René Descartes.
    • Before Galileo, it had been thought that all horizontal motion required a direct cause. Still, Galileo deduced from his experiments that a body in motion would remain in motion unless a force (such as friction) caused it to come to rest.
  • Newton’s second law is a quantitative description of the changes that a force can produce in a body's motion.
    • It states that the time rate of change of a body's momentum is equal in both magnitude and direction to the force imposed on it.
    • The momentum of a body is equal to the product of its mass and its velocity. Momentum, like velocity, is a vector quantity, having both magnitude and direction.
    • A force applied to a body can change the magnitude of the momentum, direction, or both.
    • For a body whose mass m is constant, it can be written in F = ma, where F (force) and an (acceleration) are vector quantities.
    • If a body has a net force acting on it, it is accelerated by the equation. Conversely, if a body is not accelerated, there is no net force acting on it.
  • Newton’s third law states that when two bodies interact, they apply forces to one another that are equal in magnitude and opposite in direction.
  • The third law is also known as the law of action and reaction. This law is important in analyzing static equilibrium problems, where all forces are balanced, but it also applies to bodies in uniform or accelerated motion.
  • The forces it describes are real ones, not mere bookkeeping devices. For example, a book resting on a table applies a downward force equal to its weight on the table.
  • According to the third law, the table applies an equal and opposite force to the book. This force occurs because the book's weight causes the table to deform slightly so that it pushes back on the book like a coiled spring.

The correct answer is At the centre of the Earth.

• The centre of the Earth is such that if we are at that place, the mass around us can be considered to be condensed at the surface of the Earth itself, i.e considering the Earth as a spherical shell.
• Inside a spherical shell, there is no change in potential as one moves inside, and since only a change in potential implies a force there is no force.
• Hence the acceleration due to gravity is zero at the centre of the Earth.

The correct answer is Gamma Rays.

Key Points

• 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.

Additional Information

•  Other radiations in the Electromagnetic spectrum are:

The correct answer is 342 m.

CONCEPT:

• Echo: If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo.
  • Echoes are heard due to the phenomenon of Reflection of sound waves.
  • To hear the echo clearly, the reflecting object must be more than 17.2 m from the sound source for the echo to be heard by a person standing at the source.

CALCULATION:

Speed of sound = 342 m/s.

The time is taken for hearing an echo = 2s.​

• The speed of sound is

\(⇒ Speed (v)= \frac{distance (d)}{time (t)}\)

Distance travelled = 2d = v × t

⇒ 2 × d = 342 × 2

⇒ d = (342 × 2)/2

The correct answer is the Microwave.

Key Points

• A microwave oven uses microwaves to heat food.
• In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz).
• Radio waves in this frequency range absorbed by water, fats, and sugars. When they are absorbed they are converted directly into atomic motion or vibration.
• Therefore heavy motion or vibration is converted into heat.

Important Points

• Microwaves are not absorbed by most plastics, glass, or ceramics.
• The frequency of the Microwave equals the resonance frequency of water. Therefore foods could be heated up by the oscillation of water molecules.

Additional Information

• An Electric heater, Electric blub (with filament), Electric iron is the electrical device that converts an electric current into heat.
• They working on the principle of the Joule heating effect.
  • An electric current passing through a resistor will convert that electrical energy into heat energy.

The correct answer is 12250 W.

Concept:

• Power: Power is the amount of energy transferred or converted per unit time.
  • The unit of power is watt or J/s.
  • Its dimensional formula is: [M L² T^-3].

Calculation:

Given: v = 700 m/s, m = 50 g = 0.05 kg, n/t = 60 bullets/min ⇒  1 bullet/s

The power developed by the gun is given by formula -

Power = Work done / time = Energy consumed / time

\(Power = n \times \frac{{\frac{1}{2}m{v^2}}}{t}\)

\(Power = \frac{n}{t}\; \times \frac{1}{2}m{v^2}\)

\(Power = 1 \times \frac{1}{2} \times 0.05 \times {700^2}\)

Power = 12250 watt

Calculations:

Given,

Distance of the object from the lens = u = -10 cm

Refractive index of the lens = µ = 1.5

The Radii of curvature of the lens are 20 cm in magnitude

R₁ = 20 cm and R₂ = -20 cm          (As per sign convention)

According to Len's Maker's formula

\(\frac{1}{f}=(\mu - 1)(\frac{1}{R_1}-\frac{1}{R_2})=(1.5-1)(\frac{1}{20}-\frac{1}{-20})\\ =0.5 \times \frac{2}{20}=\frac{1}{20}\\ or, \; f=20 \; cm \)

From the Lens equation,

\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\\ \frac{1}{v}=\frac{1}{f}+\frac{1}{u}\\ or, \; v=\frac{fu}{u+f}=\frac{20 \times (-10)}{-10+20}=\frac{-200}{10}=-20 \; cm\)

The image is formed 20 cm on the same side as the object.

The correct answer is 10-4 microns.

Key Points

Read the question ,it is asking value  in microns not meter.

If asked in meters then the value will be 1 Angstroms  = 10^-10 m.

But asked in microns

• 1 mm = 10^-3 m
• 1 micron = 10^-3 mm
  • ⇒ 1 micron = 10-6 m
• 1 Angstrom = 10^-10 m
  • 1 Angstrom = 10-10 m = 10-10 × 106 micron = 10-4 micron.

Confusion Points

1 Angstrom = 10^-10 meter

1 Angstrom =  10^-4 micron

Additional Information

• An Angstrom is a unit of length used to measure very small distances.
• 1 Angstroms to = 0.0001 Microns 
• It is named after Anders Jonas Ångström (Swedish physicist).
• A micron is one-millionth of a meter (10−6 m) and one Angstrom is 10-4 micron.

The correct answer is Ohm.

Key Points

• Impedance is the total sum of resistance and reactance.
• The SI Unit of Impedance(Z), resistance(R), and reactance(X) is Ohm(Ω).
• Reactance is a kind of imaginary resistance offered by electrical components like Capacitance and Inductor.
  • Reactance offered by the Inductor is called Inductive reactance, given as X_L = 2πfL.
  • Reactance offered by the Capacitor is called Capacitor reactance, given as  \(X_{C}=\frac{1}{2\pi fC}\).
  • Where 'f' - frequency of the source, 'L' - Inductance, and 'C' - Capacitance.

Additional Information