The below picture shows a mother pushing her daughter sitting on a swing. The swing is going through the positions A, B, C where A and C are extreme positions and B is the mean position.

(a) Which is the right position i.e. at A, B or C, for the mother to give a constant periodic push to the swing every time in the forward direction to increase the amplitude of the swing?

(b) Name the phenomenon involved in this.

(c) Explain with this example how this phenomenon helps to increase the amplitude of the swing.

The circuit depicted in the figure is employed for studying Ohm's Law. Instead of using a standard resistor, a student opts for a glass tube filled with mercury (tube 1), connected to the circuit through two electrodes E1 & E2. He records the readings of the ammeter and voltmeter, thereby calculates the resistance. The student repeats the experiment by substituting tube 1 with tube 2, where the same amount of mercury fills the tube 2.

Neglecting internal resistance of the cell use (> or < or =) to compare

(a) the resistance in both the cases.

(b) the voltmeter readings in both the cases.

(c) the specific resistance in both the cases.

A nichrome wire X with length (l) & cross-sectional area (A) is connected to a 10 V source and another nichrome wire Y with length (2l) & cross-sectional area (A/2), is connected to a 20 V source.

(a) Compare the resistances of wires X and Y. [Given that the resistivity of nichrome is (ρ).]

(b) Compare the electrical power consumed by each wire.

(c) Compare the masses of these wires. (Given that the density of nichrome is d.)

(d) State True or False : Wire X and wire Y both show the same rise in temperature in the same time.

Three bulbs of powers P₁, P₂ and P₃ (P₁ < P₂ < P₃) are connected in a certain way that P₃ glows brightest.

(a) What type of connection exists between these bulbs?

(b) Compare the voltage across these bulbs. (Use >, < or =)

(c) Will the circuit still function if one of the bulbs is fused?