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JEE Physics

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

434 Q 9 Topics Take Test
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Difficulty: All Easy Medium Hard 41–50 of 434
Topics in JEE Physics
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
Q.48 Medium Semiconductors
A photodiode is reverse-biased to operate in photoconductive mode. What is the primary advantage of this configuration over photovoltaic mode?
A Higher output voltage
B Faster response time and reduced noise
C Lower cost of fabrication
D Better temperature stability
Correct Answer:  B. Faster response time and reduced noise
EXPLANATION

In photoconductive (reverse-bias) mode, the depletion region widens significantly, reducing junction capacitance and transit time, resulting in faster response (MHz to GHz range) and shot noise is suppressed due to the reverse field.

Test
Q.49 Medium Semiconductors
In a p-n junction diode, the depletion width is primarily determined by which of the following factors?
A Applied voltage and doping concentrations
B Temperature and forward bias only
C Reverse bias voltage only
D Thermal energy of charge carriers
Correct Answer:  A. Applied voltage and doping concentrations
EXPLANATION

The depletion width W = √(2εε₀(V_bi + V_R)/(eN_D N_A/(N_D + N_A))) depends on applied voltage, doping concentrations, and built-in potential. Both doping levels and reverse bias voltage are critical factors.

Test
Q.50 Medium Semiconductors
A solar cell operates as a p-n junction under illumination. The maximum power output occurs at:
A Open circuit voltage (V_oc)
B Short circuit current (I_sc)
C A point between V_oc and I_sc on the I-V curve
D Zero voltage and current
Correct Answer:  C. A point between V_oc and I_sc on the I-V curve
EXPLANATION

Maximum power point (MPP) occurs where P = V × I is maximum, typically at ~80% of V_oc and ~80% of I_sc, determined by the fill factor.

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