The condition under which a microwave oven heats up a food item containing water molecules most efficiently is
Options
(a) the frequency of the microwave must match the resonant frequency of the water […]
The electromagnetic waves detected using a thermopile and used in physical therapy are
Options
(a) gamma radiations (b) x-rays (c) ultraviolet radiations (d) infrared radiations
Correct Answer:
infrared radiations
Explanation:
The electromagnetic waves […]
In electromagnetic spectrum, the frequencies of γ-rays and x-rays and ultraviolet rays are denoted by n₁,n₂ and n₃ respectively, then
Options
(a) n₁>n₂>n₃ (b) n₁n₃
Explanation:
Frequency range of ultraviolet rays ≃ 10¹⁶ […]
A plane electromagnetic wave of frequency 20 MHz travels through a space along x-direction. If the electric field vector at a certain point in space is 6 Vm⁻¹, then what is the magnetic field vector […]
The speed of electromagnetic waves in vaccum is equal to
Options
(a) μ₀ε₀ (b) √(μ₀ε₀) (c) 1/√(μ₀ε₀) (d) 1/(μ₀ε₀)
Correct Answer:
1/√(μ₀ε₀)
Explanation:
According to Maxwelll, it is found that the electromagnetic waves […]
The energy of the em waves is of the order of 15 keV. To which part of the spectrum does it belong?
Options
(a) ultraviolet rays (b) γ-rays (c) X-rays (d) Infra-red rays
Correct […]
Light with an energy flux of 25×10⁴ 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
Options
A leaf which contains only green pigments is illuminated by a laser light of wavelength 0.6328 μm. It would appear to
Options
(a) black (b) green (c) brown (d) red
Correct Answer:
black
In case of linearly polarised light, the magnitude of the electric field vector
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(a) does not change with time (b) varies periodically with time (c) is parallel to the direction of propagation […]
The electric vector vibration of an electromagnetic wave is given by E=(50 NC⁻1) sin ω(t-x/c). The intensity of the wave is
Options
(a) 2.3 Wm⁻² (b) 4.3 Wm⁻² (c) 3.3 Wm⁻² (d) 1.8 Wm⁻²
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