Physics Syllabus (JEE Main)
Q. In a circuit, a capacitor is charged and then discharged through a resistor. What is the time constant of the circuit?
A.
RC
B.
C/R
C.
R/C
D.
1/RC
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Solution
The time constant (τ) of an RC circuit is given by τ = R * C.
Correct Answer: A — RC
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Q. In a circuit, if a capacitor is fully charged, what is the voltage across it?
A.
Zero
B.
Equal to the source voltage
C.
Half of the source voltage
D.
Double the source voltage
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Solution
When a capacitor is fully charged, the voltage across it is equal to the voltage of the source it was connected to.
Correct Answer: B — Equal to the source voltage
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Q. In a circuit, if the voltage across a resistor is 12V and the current through it is 3A, what is the resistance?
A.
4 ohms
B.
3 ohms
C.
2 ohms
D.
1 ohm
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Solution
Using Ohm's law, R = V/I = 12V / 3A = 4 ohms.
Correct Answer: A — 4 ohms
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Q. In a circuit, if the voltage across a resistor is doubled, what happens to the current through it?
A.
Doubles
B.
Halves
C.
Remains the same
D.
Quadruples
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Solution
According to Ohm's law, if voltage is doubled and resistance remains constant, current also doubles.
Correct Answer: A — Doubles
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Q. In a circuit, if the voltage is halved and the resistance remains constant, what happens to the current?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
According to Ohm's law, if voltage is halved while resistance remains constant, current also halves.
Correct Answer: B — It halves
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Q. In a circuit, if the voltage is increased from 5V to 15V while the resistance remains constant at 5 ohms, what is the change in current?
A.
Increases by 1 A
B.
Increases by 2 A
C.
Increases by 3 A
D.
Increases by 4 A
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Solution
Initial current I1 = 5V / 5Ω = 1 A; Final current I2 = 15V / 5Ω = 3 A; Change in current = I2 - I1 = 3 A - 1 A = 2 A.
Correct Answer: C — Increases by 3 A
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Q. In a circuit, if the voltage is increased while keeping the resistance constant, what happens to the current?
A.
It decreases
B.
It increases
C.
It remains constant
D.
It becomes zero
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Solution
According to Ohm's Law, if voltage increases and resistance remains constant, the current will increase.
Correct Answer: B — It increases
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Q. In a circuit, if the voltage is increased while the resistance remains constant, what happens to the current?
A.
It decreases
B.
It increases
C.
It remains the same
D.
It becomes zero
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Solution
According to Ohm's Law, if the voltage (V) increases and resistance (R) remains constant, the current (I) increases.
Correct Answer: B — It increases
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Q. In a circuit, two capacitors of capacitance 2μF and 3μF are connected in parallel. What is the total capacitance?
A.
5μF
B.
6μF
C.
1.2μF
D.
0.6μF
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Solution
The total capacitance C_total in parallel is the sum of individual capacitances: C_total = C1 + C2 = 2μF + 3μF = 5μF.
Correct Answer: A — 5μF
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Q. In a circuit, two capacitors of capacitance 3μF and 6μF are connected in parallel. What is the total capacitance?
A.
9μF
B.
2μF
C.
18μF
D.
1μF
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Solution
In parallel, the total capacitance is the sum: C_total = C1 + C2 = 3μF + 6μF = 9μF.
Correct Answer: A — 9μF
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Q. In a circuit, two capacitors of capacitance 4μF and 6μF are connected in parallel. What is the total capacitance?
A.
10μF
B.
24μF
C.
2.4μF
D.
0.4μF
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Solution
For capacitors in parallel, the total capacitance is the sum of the individual capacitances: C_total = C1 + C2 = 4μF + 6μF = 10μF.
Correct Answer: A — 10μF
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Q. In a circular loop of radius R carrying a current I, what is the magnetic field at the center of the loop according to the Biot-Savart Law?
A.
B = (μ₀I)/(2R)
B.
B = (μ₀I)/(4R)
C.
B = (μ₀I)/(R)
D.
B = (μ₀I)/(πR)
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Solution
The magnetic field at the center of a circular loop of radius R carrying current I is given by B = (μ₀I)/(2R).
Correct Answer: A — B = (μ₀I)/(2R)
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Q. In a circular loop of radius R carrying a current I, what is the magnetic field at the center of the loop?
A.
μ₀I/(2R)
B.
μ₀I/(4R)
C.
μ₀I/(2πR)
D.
μ₀I/(4πR)
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Solution
The magnetic field B at the center of a circular loop of radius R carrying current I is given by B = μ₀I/(2R).
Correct Answer: A — μ₀I/(2R)
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Q. In a circular path of radius r around a long straight wire carrying current I, what is the line integral of the magnetic field?
A.
0
B.
μ₀I
C.
μ₀I/2
D.
μ₀I/4
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Solution
The line integral of B around the path is equal to μ₀I by Ampere's Law.
Correct Answer: B — μ₀I
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Q. In a closed container, if the temperature of a gas is increased, what happens to the pressure?
A.
It decreases
B.
It increases
C.
It remains constant
D.
It becomes zero
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Solution
According to Gay-Lussac's Law, if the temperature of a gas increases in a closed container, the pressure increases.
Correct Answer: B — It increases
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Q. In a closed container, if the temperature of a gas is increased, what happens to the pressure if the volume is constant?
A.
Pressure decreases
B.
Pressure increases
C.
Pressure remains constant
D.
Pressure becomes zero
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Solution
According to Gay-Lussac's Law, if the volume is constant, increasing the temperature increases the pressure.
Correct Answer: B — Pressure increases
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Q. In a closed loop circuit, if the sum of the currents entering a junction is 10A and the sum of the currents leaving the junction is 6A, what is the current flowing through the junction?
A.
4A
B.
6A
C.
10A
D.
16A
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Solution
According to Kirchhoff's current law, the current flowing into the junction must equal the current flowing out. Therefore, 10A - 6A = 4A is the current flowing through the junction.
Correct Answer: A — 4A
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Q. In a closed loop circuit, if the sum of the voltage rises is 10V and the sum of the voltage drops is 6V, what is the net voltage in the loop according to Kirchhoff's Voltage Law?
A.
4V
B.
6V
C.
10V
D.
16V
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Solution
According to Kirchhoff's Voltage Law, the net voltage in the loop is the sum of rises minus the sum of drops: 10V - 6V = 4V.
Correct Answer: A — 4V
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Q. In a closed loop circuit, if the sum of the voltage rises is 20V and the sum of the voltage drops is 15V, what is the net voltage in the loop according to Kirchhoff's Voltage Law?
A.
5V
B.
15V
C.
20V
D.
35V
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Solution
According to Kirchhoff's Voltage Law, the net voltage in the loop is the sum of voltage rises minus the sum of voltage drops: 20V - 15V = 5V.
Correct Answer: A — 5V
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Q. In a closed loop, if the net current is zero, what can be said about the magnetic field according to Ampere's Law?
A.
The magnetic field is zero everywhere
B.
The magnetic field is uniform
C.
The magnetic field can be non-zero
D.
The magnetic field is only zero at the center
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Solution
According to Ampere's Law, if the net current through a closed loop is zero, the line integral of the magnetic field around that loop is also zero, but the magnetic field can still be non-zero in some regions.
Correct Answer: C — The magnetic field can be non-zero
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Q. In a closed system, if 500 J of heat is added and 200 J of work is done by the system, what is the change in internal energy?
A.
300 J
B.
500 J
C.
700 J
D.
200 J
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Solution
According to the first law of thermodynamics, ΔU = Q - W. Here, ΔU = 500 J - 200 J = 300 J.
Correct Answer: A — 300 J
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Q. In a closed system, if the internal energy of the system increases, what can be said about the work done and heat transfer?
A.
Work done is positive, heat is absorbed
B.
Work done is negative, heat is released
C.
Work done is zero, heat is zero
D.
Work done is positive, heat is released
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Solution
According to the first law of thermodynamics, if the internal energy increases, it implies that either work is done on the system or heat is absorbed.
Correct Answer: A — Work done is positive, heat is absorbed
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Q. In a closed system, if the temperature of an ideal gas is doubled while keeping the pressure constant, what happens to its volume?
A.
It halves
B.
It doubles
C.
It remains the same
D.
It quadruples
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Solution
According to Charles's Law, V1/T1 = V2/T2. If T2 = 2T1, then V2 = 2V1.
Correct Answer: B — It doubles
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Q. In a closed system, if the temperature of an ideal gas is doubled while keeping the volume constant, what happens to the pressure?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
According to Gay-Lussac's law, pressure is directly proportional to temperature at constant volume. Therefore, if the temperature doubles, the pressure also doubles.
Correct Answer: A — It doubles
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Q. In a closed system, if the temperature of an ideal gas is doubled while the volume remains constant, what happens to the pressure?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
According to Gay-Lussac's law, pressure is directly proportional to temperature at constant volume. Therefore, if the temperature doubles, the pressure also doubles.
Correct Answer: A — It doubles
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Q. In a closed system, if the volume of the gas is doubled at constant temperature, what happens to the pressure?
A.
Doubles
B.
Halves
C.
Remains constant
D.
Increases four times
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Solution
According to Boyle's Law, at constant temperature, if the volume of a gas is doubled, the pressure is halved.
Correct Answer: B — Halves
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Q. In a communication system, if the signal-to-noise ratio (SNR) is 20 dB, what is the linear SNR?
A.
10
B.
20
C.
100
D.
200
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Solution
Linear SNR = 10^(SNR(dB)/10) = 10^(20/10) = 100.
Correct Answer: C — 100
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Q. In a communication system, what does 'multiplexing' refer to?
A.
Combining multiple signals into one
B.
Separating signals
C.
Amplifying signals
D.
Encoding signals
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Solution
Multiplexing refers to combining multiple signals into one for transmission.
Correct Answer: A — Combining multiple signals into one
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Q. In a communication system, what does 'noise' refer to?
A.
The desired signal
B.
Unwanted disturbances that affect the signal
C.
The modulation technique used
D.
The bandwidth of the channel
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Solution
Noise refers to unwanted disturbances that interfere with the desired signal, affecting the quality of communication.
Correct Answer: B — Unwanted disturbances that affect the signal
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Q. In a communication system, what does 'signal-to-noise ratio' (SNR) measure?
A.
The strength of the signal relative to background noise
B.
The total power of the signal
C.
The bandwidth of the communication channel
D.
The efficiency of the modulation technique
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Solution
Signal-to-noise ratio (SNR) measures the strength of the signal relative to the background noise, indicating the quality of the communication.
Correct Answer: A — The strength of the signal relative to background noise
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