A ²¹⁰₈₄Po nucleus undergoes alpha decay. The resulting nucleus is:

The correct answer is A: ²⁰⁶₈₂Pb. Alpha decay: A decreases by 4, Z decreases by 2. ²¹⁰₈₄Po → ²⁰⁶₈₂Pb + ⁴₂He. The resulting nucleus is Lead-206.

A parallel plate capacitor has plates of area A separated by distance d. If a dielectric of constant K is inserted between the plates, the capacitance becomes:

The correct answer is B: C = Kε₀A/d. Capacitance with dielectric: C = Kε₀A/d, where K is the dielectric constant. The dielectric increases capacitance by a factor of K

A 60W bulb and a 100W bulb are connected in series across a 200V supply. Which bulb glows brighter?

The correct answer is A: 60W bulb. In series, same current flows through both. Power = I²R. The 60W bulb has higher resistance (rated at lower power), so it dissipates more power and glows brighter

A heat engine operates between two reservoirs at temperatures 500 K and 300 K. What is the maximum theoretical efficiency of this engine?

The correct answer is A: 40%. Maximum efficiency (Carnot efficiency) = 1 - (T_cold/T_hot) = 1 - (300/500) = 1 - 0.6 = 0.4 = 40%

A monochromatic light source of wavelength λ is incident on a diffraction grating with 500 lines/mm. The second-order maximum is at 30°. What is the wavelength?

The correct answer is A: 500 nm. Grating equation: d·sin(θ) = m·λ. Here d = 1/(500 × 10³) = 2 × 10⁻⁶ m. For m = 2: (2 × 10⁻⁶)·sin(30°) = 2·λ. (2 × 10⁻⁶)·(0.5) = 2·λ. λ = 500 nm.

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JEE Physics
Waves

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

37 Q 9 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 37

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.11 Easy Waves

A person hears sound from two sources with frequencies 400 Hz and 404 Hz. The beat frequency heard is:

A 2 Hz

B 4 Hz

C 8 Hz

D 802 Hz

Correct Answer: B. 4 Hz

EXPLANATION

Beat frequency = |f₁ - f₂| = |400 - 404| = 4 Hz

Test

Q.12 Easy Waves

Standing waves are formed on a string by superposition of two waves traveling in opposite directions with:

A Same amplitude and frequency, different velocities

B Different amplitudes and same frequency

C Same amplitude, frequency, and wavelength

D Same wavelength but different frequencies

Correct Answer: C. Same amplitude, frequency, and wavelength

EXPLANATION

Standing waves form from superposition of two waves with equal amplitude, frequency, and wavelength traveling in opposite directions

Test

Q.13 Easy Waves

A longitudinal wave has frequency 50 Hz and wavelength 8 m. The wave velocity is:

A 400 m/s

B 300 m/s

C 200 m/s

D 100 m/s

Correct Answer: A. 400 m/s

EXPLANATION

v = fλ = 50 × 8 = 400 m/s

Test

Q.14 Easy Waves

A string of length 1 m is fixed at both ends. The fundamental frequency is 100 Hz. What is the frequency of the third harmonic?

A 100 Hz

B 200 Hz

C 300 Hz

D 400 Hz

Correct Answer: C. 300 Hz

EXPLANATION

For a string fixed at both ends, f_n = n × f₁. Third harmonic: f₃ = 3 × 100 = 300 Hz

Test

Q.15 Easy Waves

Two waves of equal amplitude and slightly different frequencies are superposed. The resulting pattern is called:

A Interference

B Beats

C Resonance

D Diffraction

Correct Answer: B. Beats

EXPLANATION

When two waves of slightly different frequencies interfere, alternating constructive and destructive interference produces beats with beat frequency = |f₁ - f₂|

Test

Q.16 Easy Waves

The equation of a wave is y = 0.06 sin(100t - 8x), where x and y are in meters and t is in seconds. The wavelength is:

A 0.785 m

B 1.57 m

C 2.36 m

D 3.14 m

Correct Answer: A. 0.785 m

EXPLANATION

From equation, wave number k = 8 rad/m. λ = 2π/k = 2π/8 = 0.785 m

Test

Q.17 Easy Waves

A harmonic wave travels along a string with amplitude 2 cm and wavelength 40 cm. If the wave completes 10 oscillations in 5 seconds, what is the wave velocity?

A 80 cm/s

B 120 cm/s

C 160 cm/s

D 200 cm/s

Correct Answer: A. 80 cm/s

EXPLANATION

Frequency f = 10/5 = 2 Hz, λ = 40 cm, v = fλ = 2 × 40 = 80 cm/s

Test

Q.18 Easy Waves

The intensity of a sound wave is inversely proportional to which of the following?

A Amplitude squared

B Distance squared from point source

C Frequency squared

D Wavelength

Correct Answer: B. Distance squared from point source

EXPLANATION

For a point source, intensity I ∝ 1/r². This is the inverse square law for spherical waves

Test

Q.19 Easy Waves

A longitudinal wave has a wavelength of 4 m and speed 400 m/s. The frequency of the wave is:

A 0.01 Hz

B 1600 Hz

C 100 Hz

D 400 Hz

Correct Answer: C. 100 Hz

EXPLANATION

f = v/λ = 400/4 = 100 Hz

Test

Q.20 Easy Waves

The period of a wave is 0.02 seconds. What is its frequency?

A 20 Hz

B 50 Hz

C 0.02 Hz

D 200 Hz

Correct Answer: B. 50 Hz

EXPLANATION

f = 1/T = 1/0.02 = 50 Hz

Test

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