Resistance of a System of Resistors - Resistors in Series

Name the material which is used for making the heating element of an electric iron.

A graph is plotted taking p.d. along y-axis and electric current along x-axis. Name the physical quantity that represents the slope of this graph (Fig.).

Two lamps of resistance 30Ω and 20Ω respectively are connected in series in a 110V circuit. Calculate:
(i) the total resistance in the circuit
(ii) the current in the circuit, and
(iii) the voltage drop across each lamp.

State how are the two resistors joined with a battery when equivalent resistance is more than either of the two resistances. 

If two resistors of 25 Ω and 15 Ω are joined together in series and then placed in parallel with a 40 Ω resistor, the effective resistance of the combination is : 

(a) 0.1 Ω
(b) 10 Ω
(c) 20 Ω
(d)40 Ω

Why are thick copper wires used as connecting wires?

In an electrical circuit, two resistors of 2 Ω and 4 Ω respectively are connected in series to a 6 V battery. The heat dissipated by the 4 Ω resistor in 5 s will be ______.