A magnetic dipole in a constant magnetic field has
1
zero potential energy when the torque is maximum
2
minimum potential energy when the torque is maximum
3
maximum potential energy when the torque is maximum
4
zero potential energy when the torque is minimum
Official Solution
Correct Option: (1)
Step 1: Torque on a magnetic dipole in a magnetic field is
where is the angle between and . Step 2: Torque is maximum when
Step 3: Potential energy of a magnetic dipole in a magnetic field is
Step 4: At ,
Step 5: Hence, when the torque is maximum, the potential energy is zero.
02
PYQ 2022
medium
physicsID: lpunest-
A proton accelerated by a potential difference moves through a transverse magnetic field as shown in the figure. The width of the magnetic field region is . Then the angle through which the proton deviates from the initial direction of its motion is (approximately)
1
2
3
4
Official Solution
Correct Option: (2)
Step 1: Find the speed of the proton after acceleration through potential .
For a proton:
Step 2: Radius of circular path in magnetic field:
Step 3: The proton travels an arc of a circle inside the field. From geometry (see figure),
Here,
03
PYQ 2024
medium
physicsID: lpunest-
Find equivalent capacitance between points A and B. Assume each conducting plate has same dimensions and neglect the thickness of plate. It is given that
where A is the area of plates.
1
7 \mu F
2
11 \mu F
3
12 \mu F
4
15 \mu F
Official Solution
Correct Option: (3)
Step 1: From the figure, there are three capacitors formed by six plates. For plates of equal area, capacitances are proportional to . Step 2: Using the given reference:
Step 3: The three gaps in the diagram are . Therefore individual capacitances:
Step 4: These are in parallel between A and B:
Hence → (C).
04
PYQ 2024
medium
physicsID: lpunest-
When an electric heater is switched on, the current is plotted against time . Taking into account the variation of resistance with temperature, which of the following best represents the resulting curve?
1
continuously decreasing curve
2
straight line rise
3
curve bending downward
4
curve bending upward
Official Solution
Correct Option: (1)
Step 1: For heater, temperature increases with time. Step 2: Metallic resistance increases with temperature:
Step 3: Therefore current gradually decreases, not increases. Step 4: Option (A) showing decreasing current is correct.
05
PYQ 2025
medium
physicsID: lpunest-
Which of the following temperatures is the highest?
1
2
3
4
Official Solution
Correct Option: (2)
Step 1: Convert all temperatures to the same scale (Celsius). Step 2: Convert to Celsius.
Step 3: Convert to Celsius.
Step 4: Write the remaining values in Celsius. Step 5: Compare all temperatures in Celsius. The highest temperature (closest to zero) is:
But among the converted values:
Comparing all options correctly:
However, option (B) corresponds to , which is lower than . Thus, re-check: Highest = Final Answer:
06
PYQ 2025
medium
physicsID: lpunest-
Which of the following pairs may give equal numerical values of the temperature of human body?
1
Fahrenheit and Celsius
2
Celsius and Kelvin
3
Kelvin and Reaumur
4
None of these
Official Solution
Correct Option: (4)
Step 1: Recall the normal temperature of the human body. Normal human body temperature is approximately:
Step 2: Check equality of numerical values between different scales.
Fahrenheit and Celsius: They are numerically equal only at , not at body temperature.
Celsius and Kelvin:
So numerical equality is impossible.
Kelvin and Reaumur:
No numerical equality occurs at body temperature.
Step 3: Final conclusion. None of the given pairs have equal numerical values for the temperature of the human body.