A gas undergoes an isothermal process at 300 K. If the initial volume is 2 L and final volume is 5 L, what is the work done by the gas? (Take R = 8.314 J/(mol·K), n = 1 mol)

The correct answer is B: W = 3.04 kJ. For isothermal process: W = nRT ln(Vf/Vi) = 1 × 8.314 × 300 × ln(5/2) = 2494.2 × 1.609 = 3.04 kJ

When a p-n junction is reverse biased, the width of the depletion region:

The correct answer is C: Increases. Reverse bias strengthens the electric field across the junction, causing the depletion region to expand as more charge carriers are pulled away from the junction.

The resolving power of a microscope depends on:

The correct answer is B: Wavelength of light and numerical aperture. Resolving power = 1/(1.22λ/2NA). It depends on wavelength and numerical aperture (NA = n×sin(θ))

In a cyclic process, the system returns to its initial state. Which statement is always true?

The correct answer is C: Change in internal energy is zero. For a cyclic process, ΔU = 0 since initial and final states are identical. By first law: Q = ΔU + W = W

A photodiode operates in reverse bias to:

The correct answer is B: Widen the depletion region for better light collection. Reverse bias widens the depletion region, allowing photogenerated carriers throughout this region to be swept out by the electric field, improving collection efficiency and response time.

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Waves

Physics questions for JEE Main — Mechanics, Electrostatics, Optics, Modern Physics.

47 Q 9 Topics Take Mock Test

Difficulty: All Easy Medium Hard 41–47 of 47

Topics in JEE Physics

All Mechanics 100 Thermodynamics 100 Electrostatics 100 Current Electricity 100 Magnetism 100 Optics 100 Modern Physics 100 Semiconductors 100 Waves 100

Q.41 Medium Waves

Two sources of sound have intensities I₁ and I₂. The ratio of their amplitudes is:

A √(I₁/I₂)

B I₁/I₂

C (I₁/I₂)²

D I₁² + I₂²

Correct Answer: A. √(I₁/I₂)

EXPLANATION

Since I ∝ A², the ratio A₁/A₂ = √(I₁/I₂)

Test

Q.42 Medium Waves

A pipe closed at one end and open at the other has a length of 0.5 m. The fundamental frequency is (speed of sound = 340 m/s):

A 170 Hz

B 340 Hz

C 85 Hz

D 680 Hz

Correct Answer: A. 170 Hz

EXPLANATION

For closed pipe, f₁ = v/(4L) = 340/(4×0.5) = 340/2 = 170 Hz

Test

Q.43 Medium Waves

The intensity of a sound wave is I. If the amplitude is doubled and frequency is halved, the new intensity will be:

A I

B 2I

C 4I

D I/2

Correct Answer: B. 2I

EXPLANATION

Intensity ∝ A²f². New intensity = (2A)² × (f/2)² × I/(A²f²) = 4 × (1/4) × I = 2I

Test

Q.44 Medium Waves

A wave equation is given as y = 5sin(2πx/4 - 2πt/2). The amplitude and frequency are:

A Amplitude = 5 m, Frequency = 1 Hz

B Amplitude = 5 m, Frequency = 2 Hz

C Amplitude = 10 m, Frequency = 1 Hz

D Amplitude = 5 m, Frequency = 0.5 Hz

Correct Answer: A. Amplitude = 5 m, Frequency = 1 Hz

EXPLANATION

From y = Asin(2πx/λ - 2πt/T), A = 5 m, and f = 1/T = 1/2π × 2π = 1 Hz

Test

Q.45 Medium Waves

When two coherent light sources interfere, the condition for destructive interference is:

A Path difference = nλ

B Path difference = (n+1/2)λ

C Path difference = n/2 × λ

D Path difference = λ²

Correct Answer: B. Path difference = (n+1/2)λ

EXPLANATION

For destructive interference, the path difference must be odd multiples of λ/2: (2n+1)λ/2 or (n+1/2)λ

Test

Q.46 Medium Waves

A stationary observer hears a sound from an approaching source. The observed frequency is:

A Less than the actual frequency

B Greater than the actual frequency

C Equal to the actual frequency

D Zero

Correct Answer: B. Greater than the actual frequency

EXPLANATION

Doppler effect: When source approaches observer, f' = f(v)/(v-vs), which is greater than f

Test

Q.47 Medium Waves

A sound wave with frequency 500 Hz travels through air (speed = 330 m/s) and then enters water (speed = 1500 m/s). What happens to the wavelength?

A Decreases

B Increases

C Remains the same

D Becomes zero

Correct Answer: B. Increases

EXPLANATION

Frequency remains constant during refraction. λ = v/f. Since speed increases from 330 to 1500 m/s, wavelength increases proportionally

Test

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