Major Competitive Exams
Q. A circuit contains a 12 V battery and two resistors of 4 ohms and 8 ohms in series. What is the current flowing through the circuit?
A.
0.5 A
B.
1 A
C.
1.5 A
D.
2 A
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Solution
Total resistance R = 4 + 8 = 12 ohms. Current I = V/R = 12 V / 12 ohms = 1 A.
Correct Answer: B — 1 A
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Q. A circuit contains a 12V battery and two resistors of 4 ohms and 8 ohms in series. What is the total current in the circuit?
A.
1 A
B.
0.5 A
C.
2 A
D.
3 A
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Solution
Total resistance R = R1 + R2 = 4 + 8 = 12 ohms. Current I = V/R = 12V / 12 ohms = 1 A.
Correct Answer: B — 0.5 A
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Q. A circuit contains a 9V battery and two resistors in series: 3Ω and 6Ω. What is the voltage across the 6Ω resistor?
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Solution
The total resistance R_total = 3Ω + 6Ω = 9Ω. The current I = V/R_total = 9V / 9Ω = 1A. Voltage across 6Ω, V = I * R = 1A * 6Ω = 6V.
Correct Answer: A — 6V
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Q. A circuit contains a 9V battery and two resistors of 3 ohms and 6 ohms in series. What is the voltage drop across the 6 ohm resistor?
A.
3 V
B.
6 V
C.
9 V
D.
4.5 V
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Solution
Total resistance R_total = 3 + 6 = 9 ohms. Current I = V/R_total = 9V / 9Ω = 1 A. Voltage drop across 6 ohm resistor = I * R = 1 A * 6Ω = 6 V.
Correct Answer: B — 6 V
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Q. A circuit contains a 9V battery and two resistors of 3 ohms and 6 ohms in series. What is the voltage across the 6 ohm resistor?
A.
6V
B.
3V
C.
9V
D.
4.5V
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Solution
Total resistance R_total = 3 + 6 = 9 ohms. Current I = V/R_total = 9V / 9Ω = 1 A. Voltage across 6 ohm resistor = I * R = 1 A * 6Ω = 6V.
Correct Answer: A — 6V
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Q. A circuit contains a 9V battery and two resistors of 3Ω and 6Ω in series. What is the voltage across the 6Ω resistor?
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Solution
The total resistance R_total = 3Ω + 6Ω = 9Ω. The current I = V/R_total = 9V / 9Ω = 1A. Voltage across 6Ω, V = I * R = 1A * 6Ω = 6V.
Correct Answer: A — 6V
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Q. A circuit has a total resistance of 10 ohms and a current of 5 A. What is the total voltage in the circuit?
A.
50 V
B.
10 V
C.
5 V
D.
2 V
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Solution
Using Ohm's law, V = I * R = 5 A * 10 ohms = 50 V.
Correct Answer: A — 50 V
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Q. A circuit has a voltage of 12 volts and a resistance of 4 ohms. What is the current flowing through the circuit?
A.
3 A
B.
4 A
C.
2 A
D.
1 A
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Solution
Using Ohm's Law, I = V / R = 12 V / 4 Ω = 3 A.
Correct Answer: A — 3 A
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Q. A circuit has a voltage of 12V and a resistance of 4Ω. What is the current flowing through the circuit?
A.
3A
B.
4A
C.
12A
D.
48A
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Solution
Using Ohm's Law, I = V/R = 12V / 4Ω = 3A.
Correct Answer: A — 3A
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Q. A circuit has a voltage of 24 volts and a current of 6 amperes. What is the resistance?
A.
4 Ω
B.
6 Ω
C.
8 Ω
D.
12 Ω
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Solution
Using Ohm's Law, R = V / I = 24 V / 6 A = 4 Ω.
Correct Answer: A — 4 Ω
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Q. A circular loop is placed in a uniform magnetic field. If the loop is rotated about its diameter, what happens to the induced EMF?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It becomes zero
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Solution
When the loop is rotated about its diameter, the angle between the magnetic field and the normal to the loop changes, but the magnetic flux remains constant. Therefore, the induced EMF becomes zero as there is no change in magnetic flux.
Correct Answer: D — It becomes zero
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Q. A circular loop of radius R carries a current I. What is the magnetic field at the center of the loop?
A.
μ₀I/(2R)
B.
μ₀I/R
C.
μ₀I/(4R)
D.
μ₀I/(8R)
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Solution
The magnetic field at the center of a circular loop carrying current I is given by the formula B = (μ₀I)/(2R), where μ₀ is the permeability of free space.
Correct Answer: B — μ₀I/R
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Q. A circular loop of wire carries a current. What is the direction of the magnetic field at the center of the loop?
A.
Out of the plane
B.
Into the plane
C.
Clockwise
D.
Counterclockwise
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Solution
Using the right-hand rule, the magnetic field at the center of a current-carrying circular loop is directed out of the plane of the loop.
Correct Answer: A — Out of the plane
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Q. A circular loop of wire carries a current. What is the shape of the magnetic field lines inside the loop?
A.
Straight lines
B.
Concentric circles
C.
Uniform field
D.
Radial lines
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Solution
Inside a circular loop of wire carrying current, the magnetic field lines are uniform and parallel, indicating a uniform magnetic field.
Correct Answer: C — Uniform field
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Q. A circular loop of wire is placed in a uniform magnetic field. If the magnetic field is increased, what happens to the induced EMF in the loop?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Becomes zero
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Solution
According to Faraday's law of electromagnetic induction, an increase in magnetic field through the loop induces an EMF in the loop.
Correct Answer: A — Increases
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Q. A circular loop of wire is placed in a uniform magnetic field. What happens to the induced EMF if the magnetic field strength is doubled?
A.
Induced EMF is halved
B.
Induced EMF remains the same
C.
Induced EMF is doubled
D.
Induced EMF is quadrupled
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Solution
According to Faraday's law of electromagnetic induction, the induced EMF is directly proportional to the rate of change of magnetic flux. If the magnetic field strength is doubled, the induced EMF will also double.
Correct Answer: C — Induced EMF is doubled
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Q. A circular loop of wire is placed in a uniform magnetic field. What happens to the induced EMF if the area of the loop is increased?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Depends on the magnetic field strength
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Solution
According to Faraday's law of electromagnetic induction, the induced EMF is proportional to the rate of change of magnetic flux. Increasing the area increases the flux, thus increasing the induced EMF.
Correct Answer: A — Increases
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Q. A coil of wire is placed in a changing magnetic field. What happens to the induced current if the resistance of the coil is increased?
A.
Induced current increases
B.
Induced current decreases
C.
Induced current remains the same
D.
Induced current becomes zero
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Solution
According to Ohm's law, if the resistance increases while the induced EMF remains constant, the induced current will decrease.
Correct Answer: B — Induced current decreases
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Q. A coil of wire is placed in a changing magnetic field. What phenomenon is observed?
A.
Electromagnetic induction
B.
Magnetic resonance
C.
Electrolysis
D.
Thermal conduction
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Solution
According to Faraday's law of electromagnetic induction, a changing magnetic field induces an electromotive force (EMF) in the coil.
Correct Answer: A — Electromagnetic induction
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Q. A coil of wire is placed in a magnetic field. If the magnetic field strength is increased, what happens to the induced EMF?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Becomes zero
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Solution
According to Faraday's law of electromagnetic induction, an increase in magnetic field strength induces a greater EMF.
Correct Answer: A — Increases
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Q. A coil of wire is placed in a magnetic field. If the magnetic field strength is increased, what happens to the induced EMF in the coil?
A.
It increases
B.
It decreases
C.
It remains the same
D.
It becomes zero
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Solution
According to Faraday's law of electromagnetic induction, the induced EMF in a coil is directly proportional to the rate of change of magnetic flux. Increasing the magnetic field strength increases the magnetic flux, thus increasing the induced EMF.
Correct Answer: A — It increases
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Q. A coil of wire is placed in a magnetic field. If the magnetic field strength is doubled, what happens to the induced EMF?
A.
It doubles
B.
It remains the same
C.
It halves
D.
It quadruples
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Solution
Doubling the magnetic field strength will double the induced EMF, as it is directly proportional to the magnetic field strength.
Correct Answer: A — It doubles
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Q. A coil with 100 turns and an area of 0.01 m² is placed in a magnetic field of 0.5 T. What is the magnetic flux through the coil?
A.
0.5 Wb
B.
0.1 Wb
C.
0.05 Wb
D.
0.01 Wb
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Solution
Magnetic flux Φ = B * A * N = 0.5 T * 0.01 m² * 100 = 0.5 Wb.
Correct Answer: A — 0.5 Wb
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Q. A coil with 100 turns is placed in a magnetic field that changes at a rate of 0.5 T/s. What is the induced EMF in the coil?
A.
50 V
B.
100 V
C.
200 V
D.
25 V
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Solution
Using Faraday's law, EMF = -N * (dΦ/dt) = -100 * 0.5 = -50 V. The induced EMF is 50 V.
Correct Answer: B — 100 V
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Q. A coil with 100 turns is placed in a magnetic field that changes from 0.2 T to 0.5 T in 2 seconds. What is the induced EMF?
A.
15 V
B.
30 V
C.
5 V
D.
10 V
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Solution
Induced EMF (ε) = -N(dB/dt) = -100 * (0.5 - 0.2)/2 = -15 V.
Correct Answer: B — 30 V
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Q. A coil with 100 turns is placed in a magnetic field that changes from 0.5 T to 1.5 T in 2 seconds. What is the induced EMF?
A.
50 V
B.
100 V
C.
200 V
D.
400 V
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Solution
Induced EMF = -N * (ΔB/Δt) = -100 * ((1.5 - 0.5)/2) = -100 * (1/2) = -50 V. The magnitude is 50 V.
Correct Answer: B — 100 V
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Q. A composite body consists of a solid cylinder and a solid sphere, both of mass M and radius R. What is the total moment of inertia about the same axis?
A.
(7/10) MR^2
B.
(9/10) MR^2
C.
(11/10) MR^2
D.
(13/10) MR^2
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Solution
The total moment of inertia is I_cylinder + I_sphere = (1/2 MR^2) + (2/5 MR^2) = (7/10) MR^2.
Correct Answer: A — (7/10) MR^2
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Q. A concave lens has a focal length of -12 cm. What is the image distance when the object is placed at 24 cm?
A.
8 cm
B.
12 cm
C.
16 cm
D.
20 cm
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Solution
Using the lens formula, 1/f = 1/v - 1/u, we find v = 8 cm.
Correct Answer: A — 8 cm
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Q. A concave lens has a focal length of -15 cm. What is the nature of the image formed by the lens when an object is placed at 30 cm from the lens?
A.
Real and inverted
B.
Virtual and erect
C.
Real and erect
D.
Virtual and inverted
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Solution
For a concave lens, the image formed is virtual and erect when the object is placed beyond the focal length.
Correct Answer: B — Virtual and erect
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Q. A concave lens has a focal length of -20 cm. What is the nature of the image formed when an object is placed at 30 cm from the lens?
A.
Real and inverted
B.
Virtual and erect
C.
Real and erect
D.
Virtual and inverted
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Solution
For a concave lens, the image formed is virtual and erect when the object is placed at any distance.
Correct Answer: B — Virtual and erect
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