Q. No.Out of the following options which one can be used to produce a propagating electromagnetic wave?
1.
a stationary charge.
2.
a chargeless particle.
3.
an accelerating charge.
4.
a charge moving at constant velocity.
The energy of the EM waves is of the order of \(15~\mathrm{keV}\). To which part of the spectrum does it belong?
1. X-rays
2. Infrared rays
3. Ultraviolet rays
4. \(\gamma\)-rays
| 1. | gamma rays, ultraviolet, infrared, microwaves. |
| 2. | microwaves, gamma rays, infrared, ultraviolet. |
| 3. | infrared, microwave, ultraviolet, gamma rays. |
| 4. | microwave, infrared, ultraviolet, gamma rays. |
The EM wave with the shortest wavelength among the following is:
| 1. | Ultraviolet rays | 2. | \(X\)-rays |
| 3. | Gamma-rays | 4. | Microwaves |
The frequency order for \(\gamma\) - rays (\(b\)), X – rays (\(a\)), and UV – rays (\(c\)) is:
| 1. | \( b>a>c \) | 2. | \( a>b>c \) |
| 3. | \( c>b>a \) | 4. | \( a>c>b\) |
The biological importance of the ozone layer is:
| 1. | it stops ultraviolet rays. |
| 2. | ozone layer reduces the greenhouse effect. |
| 3. | ozone layer reflects radio waves. |
| 4. | ozone layer controls \(\mathrm{O}_2 / \mathrm{H}_2\) ratio in the atmosphere. |
The magnetic field in a plane electromagnetic wave is given by \(\mathrm{B}=\left(2 \times 10^{-7}\right) \mathrm{T} \sin \left(0.5 \times 10^3 \mathrm{x}+1.5 \times 10^{11} \mathrm{t}\right )\). The wavelength and frequency of the wave are respectively:
| 1. | \( 2.16 \mathrm{~cm}, 24.1 \mathrm{~GHz} \) |
| 2. | \( 0.29 \mathrm{~cm}, 13.7 \mathrm{~GHz} \) |
| 3. | \( 3.23 \mathrm{~cm}, 20.0 \mathrm{~GHz} \) |
| 4. | \( 1.26 \mathrm{~cm}, 23.9 \mathrm{~GHz}\) |
The magnetic field in a plane electromagnetic wave is given by;
\(B_y=\left(2 \times 10^{-7}\right) \sin \left(0.5 \times 10^3 {x}+1.5 \times 10^{11} {t}\right)~\text{T}\).
The expression for the electric field is:
| 1. | \(E_z=60 \sin \left(0.5 \times 10^3 x+1.5 \times 10^{11} t\right) ~\text{V/m} \) |
| 2. | \(E_z=60 \sin \left(1.5 \times 10^3 x+0.5 \times 10^{11} t\right) ~\text{V/m} \) |
| 3. | \(E_z=55 \sin \left(0.5 \times 10^3 x+1.5 \times 10^{11} t\right) ~\text{V/m} \) |
| 4. | \(E_z=55 \sin \left(1.5 \times 10^3 x+0.5 \times 10^{11} t\right) ~\text{V/m} \) |
Assume a bulb of efficiency \(2.5\%\) as a point source. The peak values of the electric field and magnetic field produced by the radiation coming from a \(100~\text{W}\) bulb at a distance of \(3~\text{m}\) are respectively:
| 1. | \( 2.5 ~\text{V/m}, ~2.2 \times 10^{-8} ~\text{T} \) |
| 2. | \( 3.6 ~\text{V/m}, ~ 3.6 ~\text{T} \) |
| 3. | \( 4.07~\text{V/m},~ 1.4 \times 10^{-8} ~\text{T}\) |
| 4. | \( 4.2 ~\text{V/m}, ~3.4 \times 10^{-6}~\text{T}\) |
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