Physics Questions & Answers - Free Online Practice

2,736.

A wave disturbance travelling in air enters a medium in which its velocity is less than that in air. Which of the following statements is true about the wave medium?

both the frequency of the wave and the wavelength are decreased

the frequency of the wave is decreased while the wavelength is increased

the frequency of the wave is unaltered while the wavelength is decreased

the frequency of the wave is decreased while the wavelength is unaltered

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Correct answer is C

No explanation has been provided for this answer.

2,737.

A light wave of frequency 5 x 10¹⁴Hz moves through water which has a refractive index of \(\frac{4}{3}\). Calculate the wavelength in water if the velocity of light in air is 3 x 10⁸ms^-1

4.5 x 10^-7m

6.0 x 10^-7m

1.7 x 10⁶m

2.2 x 10⁶m

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Correct answer is A

\(\frac{1}{4}\) = \(\frac{3 \times 10}{v}\)

v = 2.25 x 10⁸ms^-1

\(\lambda\) = \(\frac{V}{F}\)

= \(\frac{2.25 \times 10^8}{5 \times 10^14}\)

\(\lambda\) = 0.45 x 10^-6m

2,738.

Which of the following statements are correct?

i. land and sea breezes are natural convection currents.
ii. convection may occur in liquids or gasses but not in solids.
iii. the vacuum in a thermos flask prevents heat loss due to convection only.

i and ii only

i and iii only

i, ii, and iii

View answer & explanation

Correct answer is A

Real-life examples of convection:

Breeze. The formation of sea and land breeze form the classic examples of convection.
Boiling Water.
Blood Circulation in Warm-Blooded Mammals.
Air-Conditioner.
Radiator.
Refrigerator.
The vacuum between the two walls prevents heat being transferred from the inside to the outside by conduction and convection.