1) State Joule’s law of heating. list two special characteristics of a heating element wire.
An electronic iron consumed energy at the rate of 880 W when heating is at the maximum rate and 440 W when the heating is at the minimum rate. The applied voltage is 220 V. Calculate the current and resistance in each case.
2) Copper and aluminium wires are usually employed for electricity transmission Why?
3) Obtain the expression for the heat developed in a resistor by the passage of electric current through it. 220 J of heat is produced each second in a 8 ? resistor. Find the potential difference across the resistor.
4) (a) What is heating effect of current?
List two electrical appliances which work on this effect.
(b) An electric bulb is connected to a 220 V generator. If the current drawn by the bulb is 0.50 A; find its power.
(c) An electric refrigerator rated 400 W operates eight hours a day. Calculate the energy per day in kWh.
(d) State the difference between kilowatt and kilowatt hour.
e) Why is the series arrangement of appliances not used for domestic circuits?
7) How much energy is given to each coulomb of charge passing through a 6 V battery?
8) A copper wire has a diameter 0.5 mm and resistivity 1.6 10-8 ? m.
(i) What will be the length of this wire to make the resistance of 12 ??
(ii) How much will be the resistance of another copper wire of same length but half the diameter?
9) A wire of uniform cross – section and length l has a resistance of 4 ?. The wire is cut into four equal pieces. each piece is then stretched to length ‘l’. Thereafter, the four wires are joined in parallel. Calculate the net resistance.
10) Calculate the electrical energy produced in 5 minutes when a current of 2 A is sent through a conductor by a potential difference of 500 volts.
11) An electric heater draws a current of 10 A from a 220 V supply. What is the cost of using the heater 5 hours per day for 30 days if the cost of 1 unit is Rs. 2.50?
12) An electric bulb draws a current of 0.2 A when it operates at 220 V. Calculate the amount of electric charge flowing through it in 1 h.
13) An electric bulb is rated 220 V and 100 W. when it is operated on 110 V, what will be the power consumed?
14) Resistors are given as R1 = 10 ?, R2 = 20 ?, and R3 = 30 ?. Calculate the effective resistance when they are connected in series. Also calculate the current flowing when the combination is connected to a 6 V battery.
15) The filament of an electric lamp, which draws a current of 0.2 A, is used for 5 hours. Calculate the amount of charge flowing through the circuit.
16) Calculate the number of electrons passing per second through a conductor to produce a current of one ampere.
A 5 ? resistor is connected across a battery of 6 volts. Calculate
(i) The current flowing through the resistor.
(ii) The energy that dissipates as heat in 10 s.
18) You have two electric lamps having rating 40 W; 220 V and 60 W; 220 V. Which of the two has a higher resistance? Give reason for your answer. If these two lamps are connected to a source of 220 V, which will glow brighter?
19) A current of 5 ampere is passed through a conductor of 12 ohms for 2 minutes. Calculate the amount of heat produced.
20) Can you run an electric geyser with power rating 2 kW; 220 V on a 5 A line? Give reason to justify your answer.
21) A domestic electric circuit (220 V) has a 5 A fuse. How many bulbs of 100 W; 220 V rating can be safely used on this line?
22) Two bulbs A and B are rated as 90 W – 120V and 60 W – 120 V respectively. They are connected in parallel across a 120 V source. Find the current in each bulb. Which bulb will consume more energy?
23) An electric iron is rated 2 kW at 220 V. Calculate the capacity of the fuse that should be used for the electric iron.
24) For an electric heater rated 4 kW; 220 V. Calculate:
(i) the current required
ii) the resistance of the heater
(iii) the energy consumed in 1 hour.
1) R = 110 ?
7) 6 J
8) 147.3 m ,48 ?
9) 4 ?
10) 3 X 105 J
11) RS. 825
12) 720 C
13) 25 W
14) 0.1 A
15) Q = 3600 C
16) 6.25 1018 electrons
18) 1250 ?, 3056 ?
19) 3.6 104 J
20) 9.09 Amp.
22) 90.5 A, bulb A
23) 9 A