Q. No.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
Light with an energy flux of \(25\times10^4\) Wm–2 falls on a perfectly reflecting surface at normal incidence. If the surface area is \(15\) cm2, the average force exerted on the surface is:
1. \(1.25\times 10^{-6}\) N
2. \(2.50\times 10^{-6}\) N
3. \(1.20\times 10^{-6}\) N
4. \(3.0\times 10^{-6}\) N
The condition under which a microwave oven heats up a food item containing water molecules most efficiently is:
| 1. | the frequency of microwaves has no relation with the natural frequency of water molecules. |
| 2. | microwaves are heatwaves, so always produce heating. |
| 3. | infrared waves produce heating in a microwave oven. |
| 4. | the frequency of the microwaves must match the resonant frequency of the water molecules. |
1. \(\gamma , \alpha, \beta \)
2. \( \alpha, \beta , \gamma \)
3. \( \beta, \alpha , \gamma \)
4. \(\beta, \gamma, \alpha \)
| 1. | wavelength is doubled and frequency becomes half. |
| 2. | wavelength is halved and frequency remains unchanged. |
| 3. | wavelength and frequency both remain unchanged. |
| 4. | wavelength is doubled and frequency unchanged. |
1. \(2~\mathrm{m}^{-1}\)
2. \(0.5~\mathrm{m}^{-1}\)
3. \(6~\mathrm{m}^{-1}\)
4. \(3~\mathrm{m}^{-1}\)
The ratio of the amplitude of a magnetic field to the amplitude of an electric field for an electromagnetic wave propagating in a vacuum is equal to:
| 1. | reciprocal of speed of light in vacuum. |
| 2. | the ratio of magnetic permeability to the electric susceptibility of vacuum. |
| 3. | unity. |
| 4. | the speed of light in a vacuum. |
The electric and the magnetic fields, associated with an electromagnetic wave, propagating along the positive Z-axis, can be represented by:
1. \(\left [E=E_{0}\hat{k},~B=B_{0}\hat{i} \right ]\)
2. \(\left [E=E_{0}\hat{j},~B=B_{0}\hat{j} \right ]\)
3. \(\left [E=E_{0}\hat{j},~B=B_{0}\hat{k} \right ]\)
4. \(\left [E=E_{0}\hat{i},~B=B_{0}\hat{j} \right ]\)
| 1. | gamma rays, ultraviolet, infrared, microwaves. |
| 2. | microwaves, gamma rays, infrared, ultraviolet. |
| 3. | infrared, microwave, ultraviolet, gamma rays. |
| 4. | microwave, infrared, ultraviolet, gamma rays. |
Which of the following statement is false for the properties of electromagnetic waves?
| 1. | Both electric and magnetic field vectors attain the maxima and minima at the same place and same time. |
| 2. | The energy in the electromagnetic wave is divided equally between electric and magnetic vectors. |
| 3. | Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of the wave. |
| 4. | These waves do not require any material medium for propagation. |
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