Physics Questions & Answers - Free Online Practice

551.

Thermal energy added or removed from a substance that changes the state of the substance is called

latent heat

heat of reaction

calorimetry

specific heat

Correct answer is A

Latent heat is thermal energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process.

552.

A motor of a corn mill machine operates on electrical energy of $1.44 \times 10^{5}$ J. If one-quarter of the energy is wasted on sound and heat, determine the efficiency of the machine.

25%

36%

64%

75%

View answer & explanation

Correct answer is D

No explanation has been provided for this answer.

553.

Which of the following devices converts light energy to electrical energy?

Bulb

Television

Solar cell

Light emitting diode (LED)

View answer & explanation

Correct answer is C

The solar cell converts light from the sun to electricity.

554.

The diagram above illustrates a beaker of water being heated. It is observed that as the bubbles rise they get bigger in size.The reason for this observation is

water pressure on the bubbles decreases

density of water increases with rise in temperature

volume of water increases with rise in temperature

atmospheric pressure on the bubbles decreases

View answer & explanation

Correct answer is A

When a bubble is deep under water, it has both atmospheric pressure and water pressure (giving it depth), acting on it but as it rises, the water pressure decreases. At this point, the basic pressre acting on the bubble is the atmospheric pressure. Recall that pressure is inversely proportional to volume (Boyles' law), hence, the less the pressure, the more the volume

555.

A plane is inclined at an angle $\theta$ to the horizontal. Its velocity ratio is

$sin\theta$

$tan\theta$

$\frac{1}{sin\theta}$

$\frac{1}{tan\theta}$

View answer & explanation

Correct answer is C

Velocity ratio = $\frac{Effort distance}{Load distance}$