For the following question, enter the correct numerical value upto TWO decimal places. If the numerical value has more than two decimal places, round-off the value to TWO decimal places. (For example: Numeric value 5 will be written as 5.00 and 2.346 will be written as 2.35) On interchanging the resistances, the balance point of a meter bridge shifts to the left by 10 cm. The resistance of their series combination is 1 k . How much was the resistance on the left slot before interchanging the resistances? ____ .
Official Solution
Correct Option: (1)
Step 1: Let the resistance in the left slot be and that in the right slot be . Given:
Step 2: Let the initial balance point be at cm from the left end. For a meter bridge at balance:
Step 3: After interchanging the resistances, the balance point shifts 10 cm to the left. So the new balance point is at cm. Thus,
Step 4: From equations (2) and (3), solving simultaneously:
Step 5: Substitute in equation (2):
Step 6: Using equation (1):
Final Answer (up to two decimal places):
02
PYQ 2024
medium
physicsID: lpunest-
An object is placed at distance of 20 cm from a plano-convex lens of focal length 15 cm ( ). The curved surface is silvered. The image will form at
1
60 cm left of AB
2
30 cm left of AB
3
20/7 cm left on AB
4
60 cm right of AB
Official Solution
Correct Option: (2)
Step 1: For a silvered lens, the system behaves as a mirror + refraction twice. Mirror focal length of curved side:
Given lens focal cm → radius cm → cm. Step 2: First refraction (plane side) does not change convergence significantly; disturbance mainly from mirror formula. Step 3: For object at 20 cm in front of mirror of 15 cm:
Step 4: After reflection, distance from lens plane becomes 60 cm; second refraction divides by magnification of plane interface approx 2 → gives 30 cm. Hence option (B).
03
PYQ 2025
medium
physicsID: lpunest-
Which of the following is a false statement?
1
To overcome the energy crisis the use of solar cooker must be increased
2
To overcome the energy crisis more amount of non–renewable source of energy must be used
3
The re–usage of waste material as a source of energy can be done to overcome the energy crisis
4
To overcome the energy crisis water has to be saved
Official Solution
Correct Option: (2)
Step 1: Understand the concept of energy crisis. An energy crisis refers to the shortage of energy resources and the need to use them efficiently and sustainably. Step 2: Evaluate each statement.
(A) Increasing the use of solar cookers promotes renewable energy — true (B) Increasing the use of non–renewable sources worsens depletion — false (C) Using waste materials as energy (biogas, waste-to-energy) — true (D) Saving water helps in conserving hydroelectric energy — true Step 3: Final conclusion. The false statement is option .
