Electricity quiz

The SI unit of electric charge is:

A voltmeter is always connected in:

The resistance of a conductor is directly proportional to its:

1 kWh is equal to:

A piece of wire of resistance R is cut into five equal parts, which are then connected in parallel. If the equivalent resistance is R', then R/R' is:

Which of the following terms does not represent electrical power in a circuit?

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be:

The work done in moving a charge of 2 C across two points with a potential difference of 12 V is:

The material used in electric fuses has:

Two conducting wires of the same material and equal lengths and diameters are first connected in series and then in parallel to the same source. The ratio of heat produced in series to parallel combinations is:

What does an electric circuit mean? Name a device that helps maintain a potential difference across a conductor. (2 marks)

How many electrons constitute one coulomb of charge? (2 marks)

Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal? (2 marks)

Let the resistance of an electrical component remain constant while the potential difference across its ends decreases to half its former value. What change will occur in the current through it? (2 marks)

Why does the cord of an electric heater not glow while the heating element does? (2 marks)

How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V? (2 marks)

Which uses more energy: a 250 W TV set in 1 hour, or a 1200 W electric toaster in 10 minutes? (2 marks)

What is meant by saying that the potential difference between two points is 1 V? (2 marks)

How should resistors of 1 ohm, 2 ohm and 3 ohm be connected to get the maximum and the minimum possible resistance? Find both values. (2 marks)

Why is the series arrangement not used for domestic circuits? (2 marks)

100 J of heat is produced each second in a 4 ohm resistance. Find the potential difference across the resistor. (3 marks)

An electric heater of resistance 8 ohm draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater and the total heat produced. (3 marks)

Several electric bulbs designed to be used on a 220 V supply line are rated 10 W. How many such bulbs can be connected in parallel with each other across the two wires of the 220 V line if the maximum allowable current is 5 A? (3 marks)

A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 ohm resistance, which may be used separately, in series or in parallel. What are the currents in the three cases? (3 marks)

How many 176 ohm resistors (in parallel) are required to carry 5 A on a 220 V line? (3 marks)

Read the passage and answer the questions. A family uses the following appliances daily: four 40 W tube lights for 5 hours, a 1500 W geyser for 1 hour, a 100 W television for 4 hours and a 60 W fan for 10 hours. Electricity costs Rs 6 per kWh. (i) Calculate the total energy consumed per day in kWh. (ii) Calculate the electricity bill for 30 days. (iii) Suggest one way to reduce the bill and calculate the saving if the geyser is used for only 30 minutes daily. (5 marks)

Read the passage and answer the questions. A student studies the resistance of wires of the same material. Wire A has length 1 m and area of cross-section 1 mm^2. Wire B has length 2 m and the same area. Wire C has length 1 m and area 2 mm^2. (i) If the resistance of wire A is 2 ohm, find the resistances of B and C. (ii) Which wire would heat the most if the same current is passed through each? Why? (iii) Does the resistivity of the material change between the wires? Explain. (5 marks)

Read the passage and answer the questions. An electric fuse is connected in series in the live wire of a household circuit. A kitchen circuit has a 2 kW toaster and a 1 kW kettle on a 220 V line, and is protected by a 10 A fuse. (i) Calculate the current drawn when both are used together. (ii) Will the fuse blow? Explain. (iii) Why is a fuse wire made of a material with a low melting point, and why is it connected in series? (5 marks)

Read the passage and answer the questions. A circuit has a 6 V battery connected to a 3 ohm resistor in series with a parallel combination of two 6 ohm resistors. (i) Find the equivalent resistance of the parallel part. (ii) Find the total resistance and the current drawn from the battery. (iii) Find the current through each 6 ohm resistor and the potential difference across the 3 ohm resistor. (5 marks)

Read the passage and answer the questions. An electric bulb is rated 60 W, 220 V. The filament is made of tungsten, which has a very high melting point (3380 degrees C), and the bulb is filled with chemically inactive gases. (i) Calculate the resistance of the filament when the bulb glows. (ii) Calculate the current drawn by the bulb. (iii) Why is tungsten used, and why is the bulb filled with nitrogen and argon? (5 marks)

Derive an expression for the equivalent resistance of three resistors R1, R2 and R3 connected in series, using a labelled circuit diagram. Explain why the current is the same in each resistor. Then find the current when resistors of 5 ohm, 10 ohm and 15 ohm are connected in series to a 12 V battery, and the potential difference across each. (6 marks)

Derive an expression for the equivalent resistance of three resistors connected in parallel, with a labelled circuit diagram. Explain why the potential difference across each resistor is the same. Show that the equivalent resistance in parallel is less than the smallest individual resistance. (6 marks)

Describe an experiment to verify Ohm's law. Draw the circuit diagram with a nichrome wire, ammeter, voltmeter, rheostat or cells, and key, and show a sample table and V-I graph. What would the graph look like for a conductor whose resistance increases with temperature? (6 marks)

State Joule's law of heating and derive H = I^2 R t. Explain three practical applications of the heating effect of electric current: electric iron and heater, electric bulb and electric fuse. Draw a diagram of a fuse connected in a household circuit. (6 marks)

Define electric power and derive P = VI = I^2 R = V^2/R. What is the commercial unit of electrical energy, and how is it related to the joule? An electric heater rated 1000 W is used for 2 hours a day for 30 days; find the energy consumed in kWh and the cost at Rs 5 per kWh. (6 marks)