Advertisements
Advertisements
Question
A battery of e.m.f. 12V and internal resistance 1.6 Ω is connected to two resistors of 4Ω and 6Ω connected in parallel. Calculate:
(i) the current drawn from the battery,
(ii) the power dissipated in each resistor,
(ii)the total power supplied by the battery.
Advertisements
Solution
Given: E = 12V, r = 1.6 Ω, R1 = 4 Ω, R2 = 6 Ω
Equivalent resistance in parallel R = `("R"_1"R"_2)/("R"_1 + "R"_2) = (4 xx 6)/(4 + 6) = 2.4 Omega`
Total resistance of circuit = R = r = 2.4 + 1.6 = 4.0 Ω
(i) The current drawn from the battery
I = `"E"/("R" + "r") = 12/4.0 = 3.0` A
(ii) The voltage drop in internal resistance v = Ir = 3.0 × 1.6 = 4.8 V
Voltage across each resistor (connected in parallel) V = E - v = 12 - 4.8 = 7.2 V
Power dissipated in R1 = 4 Ω, P1 = `"V"^2/"R"_1 = (7.2)^2/4 = 12.96` W
Power dissipated in R2 = 6 Ω, P2 = `"V"^2/"R"_2 = (7.2)^2/6 = 8.64` W
(iii) Total power supplied by the battery P = El = 12 × 3 = 36 W.
RELATED QUESTIONS
The commercial unit of energy is :
(a) watt
(b) watt-hour
(c) kilowatt-hour
(d) kilo-joule
The table below shows the current in three different electrical appliances when connected to the 240 V mains supply:
| Appliance | Current |
| Kettle | 8.5 A |
| Lamp | 0.4 A |
| toaster | 4.8 A |
- Which appliance has the greatest electrical resistance? How does the data show this?
- The lamp is connected to the main supply by using a thin, twin-cored cable consisting of live and natural wires. State two reasons why this cable should not be used for connecting the kettle to the mains supply.
- Calculate the power rating of the kettle when it is operated from the 240 V mains supply.
- A main takes the kettle abroad where the mains supply is 120 V. What is the current is the kettle when it is operated from the 120 V supply?
An electric heater of resistance 8 Ω takes a current of 15 A from the mains supply line. Calculate the rate at which heat is developed in the heater.
Two resistors A and B of resistance 4 Ω and 6 Ω respectively are connected in parallel. The combination is connected across a 6 volt battery of negligible resistance. Calculate: (i) the power supplied by the battery, (ii) the power dissipated in each resistor.
Two resistors A and B of 4 Ω and 6 Ω, respectively are connected in parallel. The combination is connected across a 6 volt battery of negligible resistance. Calculate the power dissipated in each resistor.
A bulb is connected to a battery of e.m.f. 6V and internal resistance 2Ω A steady current of 0.5A flows through the bulb. Calculate the total energy supplied by the battery in 10 minutes.
A. bulb is rated at 100W, 250V and another one at 60W, 250V. What is the current flowing in the circuit if the two bulbs are put in series across a 220 V mains supply?
What is the commercial unit of electrical energy? Represent it in terms of joules.
If a heater coil rated lkW, 220 V is connected in series with an electric bulb of 100 W, 220 V and are supplied 200V, power consumed by the bulb in this circuit is ______.
1 kWh = ______ J.
