Physics Syllabus (JEE Main)
Q. What is the RMS speed of an ideal gas in terms of its temperature and molar mass?
A.
sqrt((3RT)/M)
B.
sqrt((2RT)/M)
C.
sqrt((RT)/M)
D.
sqrt((3M)/RT)
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Solution
The RMS speed (v_rms) of an ideal gas is given by the formula v_rms = sqrt((3RT)/M), where R is the universal gas constant, T is the absolute temperature, and M is the molar mass.
Correct Answer: A — sqrt((3RT)/M)
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Q. What is the RMS speed of an ideal gas in terms of temperature and molar mass?
A.
sqrt((3RT)/M)
B.
sqrt((RT)/M)
C.
sqrt((3kT)/m)
D.
sqrt((2RT)/M)
Show solution
Solution
The RMS speed (v_rms) of an ideal gas is given by the formula v_rms = sqrt((3RT)/M), where R is the universal gas constant, T is the temperature in Kelvin, and M is the molar mass.
Correct Answer: A — sqrt((3RT)/M)
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Q. What is the RMS value of an AC voltage given by V(t) = V0 sin(ωt)?
A.
V0
B.
V0/√2
C.
V0√2
D.
0
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Solution
The RMS value of an AC voltage is given by V_rms = V0/√2.
Correct Answer: B — V0/√2
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Q. What is the role of a commutator in a DC motor?
A.
To convert AC to DC
B.
To reverse the direction of current
C.
To increase voltage
D.
To decrease resistance
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Solution
The commutator in a DC motor reverses the direction of current in the coil every half turn, ensuring continuous rotation in one direction.
Correct Answer: B — To reverse the direction of current
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Q. What is the role of a demodulator in a communication system?
A.
To amplify the received signal
B.
To convert the modulated signal back to its original form
C.
To filter out noise from the signal
D.
To encode the signal for transmission
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Solution
A demodulator's primary function is to convert the modulated signal back to its original form so that the information can be retrieved.
Correct Answer: B — To convert the modulated signal back to its original form
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Q. What is the role of a diode in a circuit?
A.
Resistor
B.
Capacitor
C.
Current regulator
D.
Current rectifier
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Solution
A diode acts as a current rectifier, allowing current to flow in one direction while blocking it in the opposite direction.
Correct Answer: D — Current rectifier
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Q. What is the role of a diode in a semiconductor circuit?
A.
Amplification
B.
Rectification
C.
Oscillation
D.
Capacitance
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Solution
A diode is primarily used for rectification, allowing current to flow in one direction only.
Correct Answer: B — Rectification
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Q. What is the role of a fuse in an electrical circuit?
A.
To increase current
B.
To decrease voltage
C.
To protect against overload
D.
To store energy
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Solution
A fuse is designed to protect the circuit by breaking the connection when the current exceeds a certain limit.
Correct Answer: C — To protect against overload
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Q. What is the role of a moderator in a nuclear reactor?
A.
To absorb neutrons
B.
To slow down neutrons
C.
To increase the temperature
D.
To shield radiation
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Solution
The role of a moderator in a nuclear reactor is to slow down neutrons, making them more likely to induce fission in the fuel.
Correct Answer: B — To slow down neutrons
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Q. What is the role of a p-n junction in a semiconductor device?
A.
To increase resistance
B.
To create a depletion region
C.
To enhance thermal conductivity
D.
To reduce current flow
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Solution
A p-n junction creates a depletion region which is essential for the operation of diodes and transistors.
Correct Answer: B — To create a depletion region
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Q. What is the role of a semiconductor in a transistor?
A.
To store charge
B.
To amplify current
C.
To insulate
D.
To generate heat
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Solution
In a transistor, the semiconductor material is used to amplify current, allowing small input signals to control larger output signals.
Correct Answer: B — To amplify current
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Q. What is the role of a transistor in electronic circuits?
A.
Switching
B.
Amplification
C.
Signal modulation
D.
All of the above
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Solution
Transistors can perform multiple functions including switching, amplification, and signal modulation.
Correct Answer: D — All of the above
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Q. What is the role of a transponder in satellite communication?
A.
To amplify the received signal
B.
To convert signals from one frequency to another
C.
To modulate the signal for transmission
D.
To demodulate the received signal
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Solution
A transponder receives signals at one frequency, amplifies them, and then converts them to another frequency for transmission back to Earth.
Correct Answer: B — To convert signals from one frequency to another
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Q. What is the role of coherence in interference phenomena?
A.
It determines the intensity of light
B.
It ensures constant phase difference
C.
It affects the wavelength
D.
It changes the speed of light
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Solution
Coherence refers to the constant phase relationship between waves, which is essential for producing stable interference patterns.
Correct Answer: B — It ensures constant phase difference
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Q. What is the role of temperature in the behavior of semiconductors?
A.
It has no effect
B.
It decreases conductivity
C.
It increases the number of charge carriers
D.
It only affects p-type semiconductors
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Solution
Temperature increases the number of charge carriers in semiconductors, thus increasing their conductivity.
Correct Answer: C — It increases the number of charge carriers
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Q. What is the role of the coherent sources in an interference experiment?
A.
To provide different wavelengths
B.
To ensure constant phase difference
C.
To increase the amplitude
D.
To decrease the wavelength
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Solution
Coherent sources maintain a constant phase difference, which is essential for producing a stable interference pattern.
Correct Answer: B — To ensure constant phase difference
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Q. What is the role of the galvanometer in a potentiometer circuit?
A.
To measure current
B.
To measure resistance
C.
To indicate the balance point
D.
To provide a reference voltage
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Solution
The galvanometer indicates the balance point in a potentiometer circuit, showing when the potential difference across the wire equals the unknown voltage.
Correct Answer: C — To indicate the balance point
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Q. What is the role of the galvanometer in a Wheatstone bridge?
A.
To measure voltage
B.
To measure current
C.
To detect balance
D.
To provide power
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Solution
The galvanometer is used to detect whether the bridge is balanced or unbalanced.
Correct Answer: C — To detect balance
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Q. What is the role of the jockey in a potentiometer setup?
A.
To connect the circuit
B.
To measure current
C.
To find the balance point
D.
To provide a fixed voltage
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Solution
The jockey is used to find the balance point in the potentiometer setup by sliding along the wire.
Correct Answer: C — To find the balance point
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Q. What is the role of the jockey in a potentiometer?
A.
To measure current
B.
To connect the circuit
C.
To find the null point
D.
To provide a reference voltage
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Solution
The jockey is used to find the null point where the potential difference is balanced, indicating the measurement of the unknown voltage.
Correct Answer: C — To find the null point
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Q. What is the role of the phase change upon reflection in thin film interference?
A.
It enhances constructive interference
B.
It enhances destructive interference
C.
It has no effect
D.
It changes the wavelength
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Solution
A phase change of π (or half a wavelength) occurs upon reflection from a medium of higher refractive index, affecting the interference pattern.
Correct Answer: B — It enhances destructive interference
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Q. What is the role of the refractive index in thin film interference?
A.
It determines the wavelength of light
B.
It affects the phase change upon reflection
C.
It has no effect
D.
It only affects the intensity
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Solution
The refractive index affects the phase change upon reflection; a higher refractive index can lead to a phase change of π (180 degrees).
Correct Answer: B — It affects the phase change upon reflection
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Q. What is the root mean square (RMS) value of an alternating current (AC) if its peak value is 10 A?
A.
5 A
B.
7.07 A
C.
10 A
D.
14.14 A
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Solution
The RMS value of an AC is given by I_rms = I_peak / √2. Therefore, I_rms = 10 A / √2 = 7.07 A.
Correct Answer: B — 7.07 A
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Q. What is the root mean square (RMS) value of an alternating current (AC) that has a peak value of 10 A?
A.
5 A
B.
7.07 A
C.
10 A
D.
14.14 A
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Solution
The RMS value of an AC is given by I_rms = I_peak / √2. Therefore, I_rms = 10 A / √2 = 7.07 A.
Correct Answer: B — 7.07 A
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Q. What is the root mean square speed of gas molecules at temperature T?
A.
(3RT/M)^0.5
B.
(RT/M)^0.5
C.
(2RT/M)^0.5
D.
(RT/3M)^0.5
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Solution
The root mean square speed (v_rms) is given by the formula v_rms = (3RT/M)^0.5, where R is the gas constant, T is the temperature, and M is the molar mass.
Correct Answer: A — (3RT/M)^0.5
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Q. What is the root mean square speed of gas molecules directly proportional to?
A.
The square root of the temperature.
B.
The square of the temperature.
C.
The mass of the gas molecules.
D.
The volume of the gas.
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Solution
The root mean square speed of gas molecules is directly proportional to the square root of the absolute temperature, as given by the equation v_rms = sqrt(3kT/m).
Correct Answer: A — The square root of the temperature.
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Q. What is the root mean square speed of gas molecules in a container at temperature T?
A.
sqrt(3kT/m)
B.
sqrt(2kT/m)
C.
sqrt(kT/m)
D.
sqrt(3RT/M)
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Solution
The root mean square speed (v_rms) is given by the formula v_rms = sqrt(3kT/m) where k is the Boltzmann constant, T is the temperature, and m is the mass of a gas molecule.
Correct Answer: A — sqrt(3kT/m)
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Q. What is the root mean square speed of gas molecules in an ideal gas at temperature T?
A.
sqrt(3RT/M)
B.
sqrt(2RT/M)
C.
sqrt(RT/M)
D.
sqrt(3kT/m)
Show solution
Solution
The root mean square speed (v_rms) is given by the formula v_rms = sqrt(3RT/M), where R is the gas constant, T is the temperature, and M is the molar mass.
Correct Answer: A — sqrt(3RT/M)
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Q. What is the shape of a liquid droplet on a surface due to surface tension?
A.
Flat
B.
Cylindrical
C.
Spherical
D.
Cubical
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Solution
A liquid droplet takes a spherical shape because a sphere has the minimum surface area for a given volume, minimizing the energy associated with surface tension.
Correct Answer: C — Spherical
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Q. What is the shape of the equipotential surfaces around a point mass?
A.
Straight lines
B.
Parabolas
C.
Spheres
D.
Cylinders
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Solution
The equipotential surfaces around a point mass are spherical.
Correct Answer: C — Spheres
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