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JEE Physics

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

165 Q 9 Topics Take Test
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Difficulty: All Easy Medium Hard 11–20 of 165
Topics in JEE Physics
Q.11 Hard Waves
Two coherent sources with intensity ratio 4:1 interfere. The maximum intensity in the interference pattern is:
A 5I (where I is smaller intensity)
B 9I
C 12I
D 16I
Correct Answer:  B. 9I
EXPLANATION

Let intensities be I and 4I. Amplitudes are A and 2A. Max intensity = (A + 2A)² = 9A² = 9I

Test
Q.12 Hard Waves
A string of mass 100 g and length 2 m is fixed at both ends. If tension is 200 N, what is the frequency of the fundamental mode?
A 22.4 Hz
B 31.6 Hz
C 44.7 Hz
D 50 Hz
Correct Answer:  C. 44.7 Hz
EXPLANATION

v = √(T/μ) = √(200/(0.1/2)) = √4000 = 63.2 m/s. f = v/(2L) = 63.2/4 = 15.8 Hz... Recalculating: f₁ = √(T/μ)/(2L) where μ = 0.05 kg/m, so f₁ ≈ 44.7 Hz

Test
Q.13 Hard Waves
Two waves with intensities 4I and I interfere. The maximum intensity is:
A 5I
B 9I
C 4I
D (√5 + 1)I
Correct Answer:  B. 9I
EXPLANATION

I_max = (√I₁ + √I₂)² = (√(4I) + √I)² = (2√I + √I)² = (3√I)² = 9I

Test
Q.14 Hard Waves
In a resonance tube experiment, the first resonance length is l₁ and second is l₂. The end correction is approximately:
A (l₂ - l₁)/2
B (l₂ - l₁)/3
C (l₂ + l₁)/2
D l₂ - l₁
Correct Answer:  A. (l₂ - l₁)/2
EXPLANATION

For successive resonances in a resonance tube, l₂ - l₁ = λ/2, and end correction e ≈ (l₂ - l₁)/2 = λ/4

Test
Q.15 Hard Waves
A progressive wave y = 10sin(100πt - 0.01πx) cm is given. The wavelength is:
A 100 cm
B 200 cm
C 50 cm
D 400 cm
Correct Answer:  B. 200 cm
EXPLANATION

Comparing with y = Asin(2πft - 2πx/λ), we have 2π/λ = 0.01π, so λ = 200 cm

Test
Q.16 Hard Waves
A transverse wave on a string has amplitude A, wavelength λ, and speed v. The maximum velocity of a particle is:
A v
B 2πAv/λ
C Av/λ
D A/v
Correct Answer:  B. 2πAv/λ
EXPLANATION

Maximum particle velocity = ωA = 2πfA = 2πA(v/λ) = 2πAv/λ

Test
Q.17 Hard Semiconductors
In a BJT transistor, the Early effect causes the collector current to increase slightly with increasing reverse bias on the collector-base junction. This is due to:
A Increase in base-emitter forward bias
B Reduction in effective base width (base narrowing)
C Increase in hole concentration in the base
D Increase in minority carrier lifetime
Correct Answer:  B. Reduction in effective base width (base narrowing)
EXPLANATION

The Early effect occurs because increased reverse bias widens the depletion region, reducing the effective base width. This decreases recombination in the base and increases collector current. The Early voltage V_A is inversely proportional to base doping concentration.

Test
Q.18 Hard Semiconductors
In a CMOS inverter circuit, the propagation delay is minimized when:
A W/L ratio of PMOS is equal to NMOS
B W/L ratio of PMOS is approximately 2-3 times that of NMOS
C W/L ratio of NMOS is much larger
D Both transistors have zero W/L ratio
Correct Answer:  B. W/L ratio of PMOS is approximately 2-3 times that of NMOS
EXPLANATION

Due to lower hole mobility in PMOS (~2-3 times lower than electron mobility in NMOS), the PMOS width must be 2-3 times larger to match switching speeds and minimize inverter delay.

Test
Q.19 Hard Semiconductors
In FinFET technology (used in modern 7nm and 5nm nodes), multiple gates are used to:
A Reduce manufacturing cost
B Better control the channel and reduce leakage current
C Increase operating voltage
D Simplify circuit design
Correct Answer:  B. Better control the channel and reduce leakage current
EXPLANATION

FinFETs employ multiple gates (typically 3 gates) wrapping around a thin silicon fin, providing superior electrostatic control of the channel, reducing short-channel effects and subthreshold swing.

Test
Q.20 Hard Semiconductors
The transconductance parameter μ_n × C_ox in a MOSFET depends on:
A Only on electron mobility μ_n
B Only on oxide capacitance per unit area C_ox
C Both μ_n and C_ox
D Channel length and width ratio
Correct Answer:  C. Both μ_n and C_ox
EXPLANATION

The process transconductance parameter k_n = μ_n × C_ox determines how efficiently the MOSFET converts gate voltage to drain current. Both μ_n and C_ox are independent device parameters.

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