WS Household Electricity 2014 (Sol)

Chung Cheng High School (Main) Sec 2 Physics 2014

Chapter 13: Electrical Systems Name: ( ) Class: 2 _______ Date:

13.3 Household Electricity

1. Complete the sentence below.In a three pin plug, __________________________.A the neutral wire is brown and the live wire is blue in colourB the earth wire is yellow and the live wire is blue in colourC the neutral wire is red and the live wire is blue in colourD the neutral wire is blue and the live wire is brown in colour ( D )

2. Which of the following are precautions to prevent electrocution?

I. Electrical appliances or gadgets must not be used in wet places.II. Call a certified electrician to repair damaged electrical appliances or cables.

III. Do not insert any item, such as a screwdriver, into an electrical socket.

A I and II only B I and III onlyC II and III only D All of the above ( D )

3. Which of the following pair of items is able to cut off electric current in a circuit?

A The live wire and neutral wireB The fuse and circuit breakerC The live wire and fuseD The neutral wire and circuit breaker ( B )

4. The main switch in the circuit breaker _____________________.

A controls electricity to every part of the householdB controls electricity to some parts of the householdC controls the circuit breaker onlyD has to be replaced each time it trips ( A )

5. A teacher showed her class a diagram of a circuit breaker during a Science lesson. She explained to her students that a circuit breaker does not need to be replaced. A student stated that a circuit breaker consists of thin wires that melt when too much electric current passes through it. The student’s conclusion is wrong because _____________.

A a circuit breaker has thin wires that only melt at a very high temperatureB only a very strong electric current can melt the thin wiresC a circuit breaker does not have any thin wiresD a circuit breaker has thick wires instead of thin wires ( C )

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6. An electric rice cooker was returned to the shop by a customer because whenever it was switched on and touched, it gave an electric shock. If you were the electrician, what would you do to overcome this problem?

I. Place the electric rice cooker on a plastic insulating mat.

II. If the rice cooker is connected to a two-pin plug, replace it with a three-pin plug.III. Check to see that all the wires in the electric plug are connected to the correct terminals.IV. Check that the live wire is not touching the casing of the electric rice cooker.

A I, II and III only B I, II and IV onlyC II, III and IV only D All of the above ( C )

Structured Questions

1. What is Electrical Power and its unit?

Electrical power is the rate of energy conversion per unit time and unit is Watts (W).

2. Two bulbs are rated 50W and 85W.

a. Which bulb will be brighter? Explain your choice.

The 85 W bulb. It has a higher power rating.

b. Which bulb consumes more energy? Explain your choice.

The 85 W bulb. It uses more energy per unit time than the 50W bulb.

3. Calculate the electrical power rating of a 240V, 0.03A bulb.

P = VI = 240 V x 0.03 A

= 7.2 W

4. Complete the table below to determine the values of the current, resistance or power of the electrical appliances.

Voltage Current Resistance Power Time Energy(J)

Lamp 240V 0.25A 960 60W 5.0 hrs 1080000J

Television 240V 1.0A 240 240W 30 mins 432000J

Kettle 240V 8.0A 30 1920 W 15 mins 1728000J

Power (W) = Voltage (unit: V) x Current (unit: A)

Energy (J) = Power (W) x Time (s)

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5. Complete the table below to determine energy consumption in kWh of the electrical appliances.

Appliance Power (W) Time Energy(kWh)

Lamp 60 W 5.0 hrs 0.30

Television 240 W 30 mins 0.12

Kettle 1920 W 15 mins 0.480

Energy (kWh) = Power (kW) x Time (h)

6. Given that the cost of one unit of electricity is 15cents, calculate the cost of operatinga) eight 100W bulbs for 8 hours

Cost of electricity = 8 x 0.1kW x 8 hrs x $0.15 = $ 0.96

b) four 1500W air-conditioners for 14 hours

Cost of electricity = 4 x 1.5kW x 14 hours x $0.15 = $ 12.60

c) one 1000W television for 6 hours

Cost of electricity =1 x 1.0kW x 6 x 0.15 = $ 0.90

7. Calculate the electricity bill for using two 50W lamps and a 120W television for 6 hours a day for a month. Assume the month has 30 days. Cost of one unit of electricity is $ 0.13.

Cost of electricity = (2 x 0.050 + 0.12) kW x 6 hrs x 30 days x $0.13 = $ 5.15

8. If you watched a 120W television for 2 hours and used a 20W lamp for 4 hours every day for 30 days, how much would you have to pay at the end of the 30 days, assuming that the electrical energy cost 15 cents per kWh?

Cost of electricity = (4 x 0.020 + 2hrs x 0.12) kWh x 30 days x 0.15 = $ 1.44

9. Name two examples of dangerous use of electricity.

Old and frayed wires cannot be used.Connecting many appliances to the same power outlet can overload the outlet

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1 500 W = 1.5 kW remember to convert!!!!!


10. Explain why a short circuit is dangerous in the in the use of electrical appliances in homes?

It is a path of very low resistance for the current to flow through. A large current can flow through the circuit, causing the wires to become hot. This can cause a fire in the wires or appliance.

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WS Household Electricity 2014 (Sol)

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