Question 1

Which statement correctly describes a property of electromagnetic waves?

Accepted Answer

Electromagnetic waves consist of perpendicular E and B fields oscillating in phase with each other and perpendicular to the direction of propagation.

Question 2

A convex lens of focal length 10 cm is used as a simple microscope. An object is placed at 5 cm from the lens. What is the nature of the image formed?

Accepted Answer

When object distance (5 cm) is less than focal length (10 cm), a convex lens forms a virtual, erect, and magnified image on the same side as the object.

Question 3

Which of the following correctly represents the relationship between electric field (E), magnetic field (B), and velocity (c) in an electromagnetic wave?

Accepted Answer

In an electromagnetic wave, the ratio of electric field amplitude to magnetic field amplitude equals the speed of light: E/B = c.

Question 4

The frequency of an electromagnetic wave is 2 × 10¹⁵ Hz. What is the energy of a single photon of this wave? (Use h = 6.6 × 10⁻³⁴ J·s)

Accepted Answer

Photon energy E = hf = (6.6 × 10⁻³⁴) × (2 × 10¹⁵) = 1.32 × 10⁻¹⁸ J.

Question 5

The frequency of an alternating current in India is 50 Hz. What is its time period?

Accepted Answer

Time period T = 1/f = 1/50 = 0.02 s.

Question 6

The power of a lens is –5 diopters. What is its focal length and type?

Accepted Answer

Power P = 1/f in meters; f = 1/(-5) = -0.2 m = -20 cm, and negative focal length indicates a concave (diverging) lens.

Question 7

An AC circuit has a pure resistor of 50 Ω connected to an AC source of RMS voltage 200 V. What is the RMS current through the resistor?

Accepted Answer

For a pure resistive AC circuit, I_rms = V_rms/R = 200/50 = 4 A.

Question 8

The speed of electromagnetic waves in vacuum is approximately 3 × 10⁸ m/s. If the frequency of an electromagnetic wave is 6 × 10¹⁴ Hz, what is its wavelength?

Accepted Answer

Using c = fλ, wavelength λ = c/f = (3 × 10⁸)/(6 × 10¹⁴) = 5 × 10⁻⁷ m.

Question 9

An electromagnetic wave has a wavelength of 4 × 10⁻⁷ m in vacuum. To which region of the electromagnetic spectrum does it belong?

Accepted Answer

Wavelength 4 × 10⁻⁷ m (400 nm) corresponds to violet light in the visible spectrum (380–750 nm).

Question 10

According to Lenz's law, the direction of induced current in a coil is such that it:

Accepted Answer

Lenz's law states that the induced current creates a magnetic field opposing the change in magnetic flux that produced it.

Question 11

A straight conductor of length 0.8 m moves perpendicular to a magnetic field of 0.5 T with velocity 10 m/s. What is the motional EMF induced across the conductor?

Accepted Answer

Motional EMF = B × L × v = 0.5 × 0.8 × 10 = 4 V.

Question 12

The SI unit of magnetic flux is:

Accepted Answer

Magnetic flux Φ = B × A is measured in Weber (Wb), where 1 Wb = 1 T·m².

Question 13

A convex lens has a focal length of 20 cm. An object is placed at a distance of 60 cm from the lens. What is the nature and position of the image formed?

Accepted Answer

Using lens formula 1/f = 1/u + 1/v, with f = 20 cm and u = 60 cm, we get v = 30 cm; since v is positive, image is real and inverted at 30 cm.

Question 14

A concave mirror has a radius of curvature of 40 cm. An object is placed at the center of curvature. What is the magnification of the image?

Accepted Answer

When object is at center of curvature (u = R = 40 cm), the image also forms at center of curvature with magnification m = -v/u = -1 (real, inverted, same size).

Question 15

An alternating current is represented as i = 10 sin(100πt) amperes. What is the RMS value of this current?

Accepted Answer

For AC current i = I₀ sin(ωt), RMS value = I₀/√2 = 10/√2 = 5√2 A.

Question 16

A sinusoidal AC voltage has a peak value of 220 V. What is its RMS voltage?

Accepted Answer

RMS voltage = Peak voltage/√2 = 220/√2 ≈ 155.6 V.

Question 17

A coil with 200 turns has a magnetic flux change of 0.04 Wb in 0.02 seconds. Calculate the induced EMF.

Accepted Answer

Using Faraday's law for N turns: EMF = N × |ΔΦ/Δt| = 200 × (0.04/0.02) = 200 × 2 = 400 V.

Question 18

The equation of an alternating EMF is ε = 150 sin(314t) volts. What is the frequency of this AC source?

Accepted Answer

From ε = E₀ sin(ωt), ω = 314 rad/s; frequency f = ω/2π = 314/(2π) ≈ 50 Hz.

Question 19

A rectangular coil of area 0.5 m² is placed perpendicular to a magnetic field of 2 T. If the magnetic field changes to 5 T in 0.1 seconds, what is the magnitude of induced EMF?

Accepted Answer

Using Faraday's law: EMF = |ΔΦ/Δt| = |A × ΔB/Δt| = 0.5 × (5-2)/0.1 = 0.5 × 30 = 15 V.

Question 20

A concave lens has a focal length of 15 cm. An object is placed at 30 cm from the lens. What is the distance of the image from the lens?

Accepted Answer

Using 1/f = 1/u + 1/v with f = -15 cm and u = 30 cm gives 1/(-15) = 1/30 + 1/v, solving yields v = -10 cm (virtual image).

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