12.2 Problems
543
Fig. 12.14
12.20 Two heater coils of power P 1 and P 2 (resistance R 1 and R 2 , respectively)
take individually time t 1 and t 2 to boil a fixed quantity of water. Find the
time t in terms of t 1 and t 2 , when they are connected to the mains in (a)
series and (b) parallel to boil the same quantity of water.
12.21 A battery having an emf 24 V and a resistance 2 is connected to two resistances arranged (a) in series and (b) in parallel. If the resistances are 4 and
6 , respectively, calculate the watts expended in each resistance, in each of
the two cases.
[University of London]
12.22 Power at the rate of 10 4 kW has to be supplied through 30 km of cable of
resistance 0.7 /km. Find the rate of energy loss, if the power is transmitted
at 100 kV.
[University of Dublin]
12.23 Three equal resistors, connected in series across a source of emf together,
dissipate 10 W of power. What would be the power dissipated, if the same
resistors are connected in parallel across the same source of emf?
[Indian Institute of Technology 1972]
12.24 A heater is designed to operate with a power of 1000 W in a 100 V line. It is
connected in combination with a resistance of 100 and a resistance R to a
100 V mains as shown in Fig. 12.15. What should be the value of R so that
the heater operates with a power of 62.5 W?
[Indian Institute of Technology 1978]
Fig. 12.15
543
Fig. 12.14
12.20 Two heater coils of power P 1 and P 2 (resistance R 1 and R 2 , respectively)
take individually time t 1 and t 2 to boil a fixed quantity of water. Find the
time t in terms of t 1 and t 2 , when they are connected to the mains in (a)
series and (b) parallel to boil the same quantity of water.
12.21 A battery having an emf 24 V and a resistance 2 is connected to two resistances arranged (a) in series and (b) in parallel. If the resistances are 4 and
6 , respectively, calculate the watts expended in each resistance, in each of
the two cases.
[University of London]
12.22 Power at the rate of 10 4 kW has to be supplied through 30 km of cable of
resistance 0.7 /km. Find the rate of energy loss, if the power is transmitted
at 100 kV.
[University of Dublin]
12.23 Three equal resistors, connected in series across a source of emf together,
dissipate 10 W of power. What would be the power dissipated, if the same
resistors are connected in parallel across the same source of emf?
[Indian Institute of Technology 1972]
12.24 A heater is designed to operate with a power of 1000 W in a 100 V line. It is
connected in combination with a resistance of 100 and a resistance R to a
100 V mains as shown in Fig. 12.15. What should be the value of R so that
the heater operates with a power of 62.5 W?
[Indian Institute of Technology 1978]
Fig. 12.15