1.
Why does the letter \(p\) appears like \(q\) when placed infront of a plane mirror?
Exercises 6.4 Exercises
2.
Why do the stars twinkle in a night sky? How about the same stars if seen from international space station?
3.
What makes setting sun appear red?
Answer.
scattering of light from the atmospheric air molecules.
4.
Why do we see objects as white?
5.
The American flag appears when viewed in blue light.
- red and blue.
- blue and black
- all blue.
- red, white, and blue.
Hint.
White is a combination of all the colors, and black is the absense of all colors. When viewed in the blue light only blue light reflects. The blue parts are not affected, the red parts are black now, and the white parts are blue now.
6.
Find the wavelengths of sound which have a speed of \(345 m/s\) and frequencies of
- \(\displaystyle 20 Hz\)
- \(\displaystyle 20 kHz\)
7.
Which of the following is not a reason behind rainbow formation?
- Reflection.
- Refraction.
- Dispersion.
- Scattering.
8.
Scattering is responsible for the color of the daytime sky.
- red
- blue
- orange
- white
9.
Scattering occurs when light waves are forced to depart from a path due to imperfections in the medium.
- curved
- straight
- angled
10.
Refraction occurs
- when waves changed speed
- only with light waves
- at any unpredictable time
11.
What causes wet spot mirage on the high way road?
- Reflection
- Refraction
- Dispersion
- Scattering
12.
Different colors of light waves travell with different speeds in transparent medium. How they travell in vacuum?
- At different speeds.
- At same speed.
- Both a and b.
- None of the above.
13.
My radio station is tuned at 90MHz frequency. What is the wavelength of that radio wave. The velocity of electromagnetic wave is \(3\times 10^8 m/s.\)
Solution.
Given: \(f=90MHz= 90\times 10^6 Hz\text{,}\) \(v= 3\times 10^8 m/s,\text{,}\) \(\Lambda=?\)
\begin{align*}
v \amp =f\lambda \\
\lambda \amp =\frac{v}{f} \\
\lambda \amp =\frac{3\times 10^8}{90\times 10^6} \\
\therefore \lambda \amp =3.33 m
\end{align*}
