Explain the following : (a) Why is tungsten used almost exclusively for filament of electric lamps? (b) Why are the conductors of electric heating devices, such as breadtoasters and electric irons, made of an alloy rather than a pure metal? (c) Why is the series arrangement not used for domestic circuits? (d) How does the resistance of a wire vary with its area of cross-section? (e) Why are copper and aluminium wires usually employed for electricity transmission?

An electric heater of resistance 8 W draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater.

Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?

Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to the electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Compare the power used in the 2 Ω resistor in each of the following circuits: (i) A 6 V battery in series with 1 Ω and 2 Ω resistors. (ii) A 4 V battery in parallel with 12 Ω and 2 Ω resistors.

A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or parallel. What are the currents in the three cases?

Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of a 220 V line if the maximum allowable current is 5 A?

Show how you would connect three resistors, each of resistance 6 Ω so that the combination has a resistance of (i) 9 Ω, (ii) 4 Ω.

How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?

A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4Ω, 0.5Ω and 12Ω, respectively. How much current would flow through the 12Ωresistor?

When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below : I (amperes) 0.5 1.0 2.0 3.0 4.0 V (volts) 1.6 3.4 6.7 10.2 13.2 Plot a graph between V and I and calculate the resistance of that resistor.

A copper wire has a diameter of 0.5 mm and resistivity of 1.6 × 10–8Ω m. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?

How is a voltmeter connected in the circuit to measure the potential difference between two points?

Two conducting wires of the same material and equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be : (a) 1 : 2 (b) 2 : 1 (c) 1 : 4 (d) 4 : 1

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be : (a) 100 W (b) 75 W (c) 50 W (d) 25 W

Which of the following terms does not represent electrical power in a circuit? (a) I2R (b) IR2 (c) VI (d) V2/R [NCERT]

A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then the ratio R/R’ is : (a) 1/25 (b) 1/5 (c) 5 (d) 25

An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h

What determines the rate at which energy is delivered by a current

An electric iron of resistance 20 W takes a current of 5 A. Calculate the heat developed in 30 s.

Why does the cord of an electric heater not glow while the heating element does?

What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?

How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω

What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?

An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it?

Judge the equivalent resistance when the following (a) 1 Ω and 106 Ω, (b) 1 Ω and 103 Ω and 106 Ω.

Redraw the circuit of Question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the 12 W resistor. What would be the readings in the ammeter and the voltmeter?

Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 W resistor, an 8 W resistor, and a 12 W resistor, and a plug key, all connected in series.

How much energy is given to each coulomb of charge passing through a 6 V battery?

What is meant by saying that the potential difference between two points is 1 V?

Name a device that helps to maintain a potential difference across a conductor.

Calculate the number of electrons constituting one coulomb of charge.

Define the unit of current.

What does an electric circuit mean?