Physics Syllabus (JEE Main)
Q. What happens to the light intensity when it passes through two crossed polarizers?
A.
It doubles
B.
It is halved
C.
It becomes zero
D.
It remains the same
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Solution
When light passes through two crossed polarizers (90 degrees apart), no light is transmitted, resulting in zero intensity.
Correct Answer: C — It becomes zero
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Q. What happens to the light intensity when it passes through two polarizers aligned at an angle of 30 degrees?
A.
It remains the same
B.
It is halved
C.
It is reduced to one-fourth
D.
It is reduced to three-fourths
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Solution
Using Malus's law, the transmitted intensity I = I_0 * cos²(θ). For θ = 30 degrees, I = I_0 * (√3/2)² = (3/4)I_0.
Correct Answer: D — It is reduced to three-fourths
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Q. What happens to the light ray when it hits the boundary at an angle greater than the critical angle?
A.
It is refracted
B.
It is absorbed
C.
It is reflected back into the denser medium
D.
It passes into the rarer medium
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Solution
When the angle of incidence exceeds the critical angle, the light ray undergoes total internal reflection and is reflected back into the denser medium.
Correct Answer: C — It is reflected back into the denser medium
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Q. What happens to the light ray when it hits the boundary at the critical angle?
A.
It is refracted into the second medium.
B.
It is reflected back into the first medium.
C.
It travels along the boundary.
D.
It is absorbed.
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Solution
At the critical angle, the light ray is refracted at 90°, traveling along the boundary between the two media.
Correct Answer: C — It travels along the boundary.
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Q. What happens to the magnetic field inside a long solenoid when the current through it is increased?
A.
Magnetic field decreases
B.
Magnetic field remains constant
C.
Magnetic field increases
D.
Magnetic field becomes zero
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Solution
The magnetic field inside a long solenoid is directly proportional to the current flowing through it. Increasing the current increases the magnetic field strength.
Correct Answer: C — Magnetic field increases
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Q. What happens to the magnetic field inside a solenoid if the current is reversed?
A.
Reverses direction
B.
Increases
C.
Decreases
D.
Remains the same
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Solution
Reversing the current reverses the direction of the magnetic field.
Correct Answer: A — Reverses direction
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Q. What happens to the magnetic field inside a solenoid when the current flowing through it is increased?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Becomes zero
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Solution
The magnetic field inside a solenoid is directly proportional to the current flowing through it; thus, it increases with an increase in current.
Correct Answer: A — Increases
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Q. What happens to the magnetic field inside a solenoid when the current through it is increased?
A.
It decreases
B.
It remains constant
C.
It increases
D.
It becomes zero
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Solution
The magnetic field inside a solenoid is directly proportional to the current flowing through it, so increasing the current increases the magnetic field.
Correct Answer: C — It increases
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Q. What happens to the magnetic field lines when a magnet is cut in half?
A.
One magnet becomes a monopole
B.
Two smaller magnets are formed
C.
Magnetic field disappears
D.
Field lines become straight
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Solution
When a magnet is cut in half, each half becomes a smaller magnet with its own north and south poles, resulting in two smaller magnets.
Correct Answer: B — Two smaller magnets are formed
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Q. What happens to the magnetic field strength if the current in a solenoid is halved?
A.
Doubles
B.
Halves
C.
Remains the same
D.
Quadruples
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Solution
The magnetic field strength is directly proportional to the current, so it halves.
Correct Answer: B — Halves
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Q. What happens to the magnetic field strength if the distance from a long straight conductor is doubled?
A.
It doubles
B.
It halves
C.
It quadruples
D.
It becomes zero
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Solution
The magnetic field strength around a long straight conductor is inversely proportional to the distance from the conductor. Therefore, if the distance is doubled, the magnetic field strength halves.
Correct Answer: B — It halves
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Q. What happens to the magnetic field strength if the distance from a long straight wire is tripled?
A.
Increases by 3 times
B.
Decreases by 3 times
C.
Decreases by 9 times
D.
Remains the same
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Solution
The magnetic field strength decreases with the square of the distance from the wire.
Correct Answer: C — Decreases by 9 times
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Q. What happens to the magnetic field strength inside a long solenoid when the current through it is increased?
A.
It decreases
B.
It remains constant
C.
It increases
D.
It becomes zero
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Solution
The magnetic field strength inside a long solenoid is directly proportional to the current flowing through it; thus, it increases with an increase in current.
Correct Answer: C — It increases
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Q. What happens to the magnetic field strength when the distance from a long straight conductor is doubled?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
The magnetic field strength around a long straight conductor decreases inversely with distance, so it halves when the distance is doubled.
Correct Answer: B — It halves
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Q. What happens to the moment of inertia of a rigid body if it is rotated about an axis that is not its principal axis?
A.
It increases
B.
It decreases
C.
It remains the same
D.
It becomes zero
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Solution
The moment of inertia can change when rotating about an axis that is not a principal axis due to the distribution of mass relative to the new axis.
Correct Answer: A — It increases
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Q. What happens to the null point in a potentiometer if the resistance of the wire is increased?
A.
Null point moves towards the battery
B.
Null point moves away from the battery
C.
Null point remains unchanged
D.
Null point becomes unstable
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Solution
Increasing the resistance of the wire decreases the current, which causes the null point to move away from the battery.
Correct Answer: B — Null point moves away from the battery
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Q. What happens to the number of emitted electrons if the intensity of light is increased while keeping the frequency above the threshold?
A.
The number of emitted electrons decreases
B.
The number of emitted electrons increases
C.
The energy of each emitted electron increases
D.
No electrons are emitted
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Solution
Increasing the intensity of light increases the number of photons incident on the surface, leading to more emitted electrons, provided the frequency is above the threshold.
Correct Answer: B — The number of emitted electrons increases
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Q. What happens to the number of emitted electrons if the intensity of the light is increased while keeping the frequency above the threshold?
A.
The number of emitted electrons decreases
B.
The number of emitted electrons increases
C.
The energy of each emitted electron increases
D.
No effect on the number of emitted electrons
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Solution
Increasing the intensity of light increases the number of photons, which in turn increases the number of emitted electrons, provided the frequency is above the threshold.
Correct Answer: B — The number of emitted electrons increases
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Q. What happens to the photoelectric current if the voltage across the electrodes is increased?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Becomes zero
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Solution
Increasing the voltage increases the photoelectric current by attracting more emitted electrons.
Correct Answer: A — Increases
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Q. What happens to the photoelectric effect if the incident light is below the threshold frequency?
A.
Electrons are emitted
B.
No electrons are emitted
C.
Electrons are emitted with low energy
D.
Electrons are emitted with high energy
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Solution
If the incident light is below the threshold frequency, no electrons are emitted.
Correct Answer: B — No electrons are emitted
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Q. What happens to the photoelectric effect if the metal surface is cooled?
A.
More electrons are emitted
B.
Fewer electrons are emitted
C.
No effect on emission
D.
Electrons are emitted with higher energy
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Solution
Cooling the metal surface reduces the thermal energy of the electrons, making it harder for them to overcome the work function.
Correct Answer: B — Fewer electrons are emitted
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Q. What happens to the pitch of a sound as its frequency increases?
A.
It decreases
B.
It increases
C.
It remains the same
D.
It becomes inaudible
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Solution
As the frequency of a sound increases, its pitch also increases.
Correct Answer: B — It increases
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Q. What happens to the polarization of light when it passes through a polarizer at an angle of 45 degrees?
A.
It becomes unpolarized
B.
It is completely absorbed
C.
It is partially polarized
D.
It is fully polarized
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Solution
When light passes through a polarizer at an angle of 45 degrees, it becomes partially polarized.
Correct Answer: C — It is partially polarized
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Q. What happens to the potential difference across a capacitor when it is fully charged?
A.
It becomes zero
B.
It becomes maximum
C.
It becomes minimum
D.
It fluctuates
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Solution
When a capacitor is fully charged, the potential difference across its plates becomes maximum and remains constant until it is discharged.
Correct Answer: B — It becomes maximum
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Q. What happens to the potential difference across a segment of a potentiometer wire if the length of that segment is halved?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It becomes zero
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Solution
If the length of the segment is halved, the potential difference across that segment also halves, assuming the potential gradient remains constant.
Correct Answer: B — It halves
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Q. What happens to the potential difference across a segment of a potentiometer wire if the resistance of the wire is increased?
A.
It increases.
B.
It decreases.
C.
It remains the same.
D.
It becomes zero.
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Solution
Increasing the resistance of the wire decreases the current, which in turn decreases the potential difference across any segment of the wire.
Correct Answer: C — It remains the same.
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Q. What happens to the pressure in a fluid as depth increases?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Varies randomly
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Solution
In a fluid at rest, pressure increases with depth due to the weight of the fluid above.
Correct Answer: A — Increases
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Q. What happens to the pressure of a gas if its temperature is increased while keeping the volume 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 temperature increases at constant volume, the pressure increases.
Correct Answer: B — Pressure increases
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Q. What happens to the pressure of a gas if its volume is halved at constant temperature?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
According to Boyle's law, if the volume is halved at constant temperature, the pressure doubles.
Correct Answer: A — It doubles
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Q. What happens to the pressure of a gas if its volume is halved while keeping the temperature constant?
A.
Pressure decreases
B.
Pressure remains the same
C.
Pressure doubles
D.
Pressure triples
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Solution
According to Boyle's law, if the volume of a gas is halved while keeping the temperature constant, the pressure doubles.
Correct Answer: C — Pressure doubles
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