The diagrams given below show two sound boxes A and B with wires of same length (l) and tension (10 kgf) but different cross-sectional areas. Simultaneously, vibrating tuning forks of frequency 300 Hz are placed on the boxes A and B. The paper rider falls off in case of B but not in case of A.

(a) Name and explain the phenomenon responsible for the falling off of the paper rider in B.

(b) The wire A resonates with a tuning fork of frequency ‘f’. Is ‘f’ greater than, less than or equal to 300 Hz? Justify your answer.

The diagram shows wiring in a meter room of a building.

(a) What is the current rating of device X?

(b) What is the difference between the switch Z shown in the diagram and the switches you use to operate different appliances at home?

(c) What is the unit of the physical quantity displayed in Y?

Three identical bulbs B₁, B₂ and B₃ each of power rating 18 W, 12 V are connected to a battery of 12 V.

(a) Calculate :

1. the resistance of each bulb
2. the current drawn from the cell

(b) If the bulb B₃ is removed from the circuit, then will the brightness of the bulb B₁ increase, decrease or remain the same?

30 g of ice at 0°C is used to bring down the temperature of a certain mass of water at 70°C to 20°C. Find the mass of water.

[Specific heat capacity of water = 4.2 J g⁻¹ °C⁻¹ and specific latent heat of ice = 336 J g⁻¹]