Test: Physics - 2 - UPSC MCQ

The minimum height of a plane mirror to see the full size image of a person is equal to the half the height of the person.

Heat to electrical energy conversion occurs in solar cell. Electric to sound occurs in loud speaker. Mass to heat occurs in nuclear reactor. Chemical to heat and light occurs in fuel burning.

Magnetic resonance imaging is based on the phenomenon nuclear magnetic resonance.

Aman is standing on a boat in still water. If he walks towards the shore, the boat will move away from the shore. This is according to Newton’s third law of motion — to every action there is equal and opposite reaction.

Correct Answer:C

An upper endoscopy is a procedure used to visually examine your upper digestive system with a tiny camera on the end of a long, flexible tube.

Basically, a typical endoscope uses fiber optics, which allow for effective transmitting of light. The optical fiber allows for light to travel through curved paths, which makes one of the best systems to view spaces that would normally be difficult to reach. Here, total internal reflection makes it possible for light to travel along the fibers with the light rays hitting the fiber walls at an angle (minimum angle of 82 degree).

After the melting of ice, the level of water remains the same because the total volume of the melted ice is equal to the volume of floating ice.

When the man tosses a coin, the coin falls behind him because the train is moving forward with acceleration.

A fan produces a feeling of comfort during hot weather because our perspiration evaporates rapidly. Evaporation process takes surroundings temperature.

A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.

A diamond sparkles more than a glass imitation cut to the same shape is only the true statement. The refractive index of diamond 2.42 > glass 1.5.

Sound waves require material medium to travel. On the surface of the moon, there is no atmosphere. The speed of sound is maximum in solids and minimum in gas medium.

Assertion (A): The temperature of a metal wire rises when an electric current is passed through it.

• This statement is true. When an electric current passes through a metal wire, the electrical resistance of the wire causes some of the electrical energy to be converted into heat energy, leading to an increase in temperature.

Reason (R): Collision of metal atoms with each other releases heat energy.

• The collision of metal atoms with each other releases heat energy. This phenomenon is called the Joule effect or Joule heating. When an electric current passes through a metal wire, the free electrons in the wire collide with the metal atoms. This collision transfers kinetic energy to the metal atoms, which manifests as heat.

Therefore, the correct answer is: Both A and R are true, but R is not the correct explanation of A.

When the person looks at a coin which is in a bucket of water, the coin will appear closer and at a higher level than it really is. µ2 = real depth / apparent depth

A stick is dipped in water in a slanting position. If observed sideways, the stick appears short and bent because of refraction of light.

Because thermal conductivity of copper is greater than glass.

Mirage is formed due to total internal reflection of light which is a phenomenon of refraction of light when it travels from a denser medium to rarer medium followed by reflection.

Radio waves are produced by rapidly oscillating electrical currents. For detecting over speeding of vehicles, police use the Doppler effect to reflected short radio waves. 

As a hydrogen-inflated polythene balloon rises to an altitude in the atmosphere, it will increase in size. This is because the atmospheric pressure decreases with increasing altitude. As the balloon ascends, the external pressure decreases while the pressure inside the balloon remains relatively constant

The free surface of oil is inclined to the horizontal with larger depth at the rear end as the oil tanker is moving forward with uniform acceleration.

The velocity of sound in air increases as the humidity increases.

Heat, like sound, is a form of kinetic energy. Molecules at higher temperatures have more energy, thus they can vibrate faster. Since the molecules vibrate faster, sound waves can travel more quickly. The speed of sound in room temperature air is 346 meters per second.

The speed of sound in air is independent of pressure, since the ratio of pressure P to density 'rho' of air is always constant for a given temperature, according to Boyle's law.