The energy released per fission of is . The fission rate of required to produce power is
1
per second
2
per second
3
per second
4
per second
Official Solution
Correct Option: (4)
Step 1: Convert energy per fission from MeV to joules.
Step 2: Power is energy released per second. Given power:
Step 3: Fission rate required:
02
PYQ 2022
medium
physicsID: lpunest-
In the following common emitter circuit, and . If is negligible, then the base current is
1
2
3
4
Official Solution
Correct Option: (2)
Step 1: From the circuit, the supply voltage is:
Collector resistance:
Step 2: Given:
Since the emitter is grounded, the collector voltage is:
Step 3: Voltage drop across the collector resistance:
Step 4: Collector current:
Step 5: Using the relation :
Step 6: The closest value among the given options is:
03
PYQ 2024
medium
physicsID: lpunest-
In a hypothetical Bohr’s hydrogen atom the mass of the electron is doubled. The energy and radius of the first orbit will be ( is the Bohr radius for the first orbit):
1
2
3
4
Official Solution
Correct Option: (3)
Step 1: Recall Bohr model dependences. For a hydrogen atom, the Bohr radius and energy depend on the reduced mass of the electron–proton system. For ordinary hydrogen:
Step 2: Effect of doubling the electron mass. If the electron mass is doubled:
Step 3: Find the new radius of the first orbit. Since:
Step 4: Find the new ground-state energy. Since:
Original ground-state energy:
With doubled mass:
Hence,
04
PYQ 2024
medium
physicsID: lpunest-
The real angle of dip at a place, if a magnet is suspended at an angle of to the magnetic meridian and the dip needle makes an angle of with the horizontal, is:
1
2
3
4
Official Solution
Correct Option: (1)
Step 1: Identify the given quantities. Angle between magnet and magnetic meridian:
Apparent angle of dip:
Step 2: Recall the relation between real dip and apparent dip. When the magnet is not in the magnetic meridian, the relation is:
where = real angle of dip. Step 3: Substitute the given values. Step 4: Solve for the real angle of dip. Hence, the real angle of dip is .
05
PYQ 2025
medium
physicsID: lpunest-
Among identical spheres A and B having charges as and :
1
is at higher potential
2
is at higher potential
3
both are at equal potential
4
it cannot be said
Official Solution
Correct Option: (1)
Step 1: Recall the formula for electric potential of a charged sphere. For a conducting sphere:
where is a constant and is the radius of the sphere. Step 2: Compare the given spheres. The spheres are identical, so their radii are the same. Hence, electric potential depends only on the charge. Step 3: Compare the charges. Since:
corresponds to a higher (less negative) potential. Step 4: Final conclusion. The sphere carrying charge is at a higher potential.
06
PYQ 2025
medium
physicsID: lpunest-
Among the following statements:
A discharge lamp uses a discharge tube which is filled with a gas at a very low pressure.
Always white light is emitted independent of gas taken in the lamp.
1
Only 1 is true
2
Only 2 is true
3
Both 1 and 2 are true
4
Both 1 and 2 are false
Official Solution
Correct Option: (1)
Step 1: Examine statement (1). A discharge lamp works by passing electric current through a gas at very low pressure inside a discharge tube (e.g., neon lamp, sodium vapour lamp). Hence, statement (1) is true. Step 2: Examine statement (2). The colour of light emitted by a discharge lamp depends on the type of gas used. For example:
Neon gas → red light
Sodium vapour → yellow light
Mercury vapour → bluish light
Therefore, white light is not always emitted. Statement (2) is false. Step 3: Final conclusion. Only statement (1) is true.
