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CBSE

NEET Physics : Electromagnetic Waves

Multiple Choice Questions

51.

The electric field associated with an electromagnetic wave in vaccum is given by E = i 40 cos (kz − 6 x 10⁸ t), where E, Z and t are in volt m^-1, metre and second respectively. The value of wave vector (k) is

2 m^-1
0.5 m^-1
6 m^-1
3 m^-1

52.

Two elements A and B with atomic numbers Z_A and Z_B are used to produce characteristic X-rays with frequencies v_A and v_B respectively. If Z_A : Z_B = 1 : 2, then v_A : v_B will be

$1 : \sqrt{2}$
1 : 8
4 : 1
1 : 4

53.

The energy of gamma (γ) ray photon is E_γ and that of an X-ray photon is E_x. If the visible light photon has an energy of E_v, then we can say that

E_X > E_γ > E_v
E_γ > E_v > E_X
E_γ > E_X > E_v
E_X > E_v > Eγ

54.

In which of the following phenomena, the heat waves travel along straight lines with the speed of light ?

Thermal conduction
Forced convection
Natural convection
Thermal radiation

55.

Electrons with de-Broglie wavelength λ fall on the target in an X-ray tube. The cut-off wavelength of the emitted X-rays is

$λ_{0} = \frac{2 {mcλ}^{2}}{h}$
$λ_{0} = \frac{2 h}{mc}$
$λ_{0} = \frac{2 m^{2} c^{2} λ^{3}}{h^{2}}$
$λ_{0} = λ$

56.

Which of the following electromagnetic waves have the smallest wavelength ?

γ-rays
X-rays
UV waves
infrared rays

57.

The condition under which a microwave oven heats up a food item containing water molecules most efficiently is

the frequency of the microwave must match the resonant frequency of the water molecules
the frequency of the microwave has no relation with natural frequency of water molecules
microwave are heat waves, so always produce heating
infrared waves produce heating in a microwave oven

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NEET Physics : Electromagnetic Waves

Multiple Choice Questions