Physics: Senior High School: 11th and 12th Grade Quiz - Electricity - Household Electricity (Questions)

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Washing machines and vacuum cleaners are two of many devices that we take for granted. Without these, our lives would be very different and household chores would take much longer. In the 1950s, very few married women went out to work. Instead they were expected to look after the husband and children and do the housework, spending 70 hours a week (that's almost twice the time of the normal working week) cleaning, cooking and shopping. One of the reasons that this changed is that electrical appliances for the home became more affordable and many new devices were invented, all taking advantage of domestic electricity.

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Actually, household electricity is the same as any other electricity - it's just an alternative way of saying electricity in the home. Electricians refer to it as a domestic supply. The first important thing to remember is that it is 230 V. This can deliver a current carrying enough energy to kill you - so knowing about electrical safety in the home is important.

Most household appliances need to be plugged into the mains. In other words, they are connected to one of the wall sockets using a plug. A lot of the plugs have three pins: live, neutral and earth. You have probably wired a plug as part of your senior high school science course and may have done it again in senior high school. Hopefully, by now you will have learned which color wires should be connected to which pins. If not then find out, as you are expected to know this for your exam. In practical terms, this is extremely useful as you may need to replace a plug on a household electrical appliance many times during your life.

The earth pin is part of the safety that is built into all household electricity systems. If an electrical fault develops in an appliance, a large current will flow through the earthing system. This will blow the fuse in the plug or, more likely, cause one of the circuit breakers to trip at the consumer unit. The consumer unit is the junction between the wiring inside the house and the outside electricity supply. When a fuse blows or a circuit breaker trips, the electricity to the appliance is cut off, making it safe. Another safety feature of any electrical system is that the wires are coated with plastic to electrically insulate them. Touching a bare wire that is connected to mains electricity is definitely not good for your health!

The electricity supplied to your home is AC, which stands for alternating current. In an alternating current the direction in which the current flows is constantly changing. In the UK it changes 50 times every second, so we say the AC has a frequency of 50 hertz (symbol Hz). This is fine for many electrical appliances, however, it is not OK for others like computers, radios and TVs. These also run off lower voltages so they are fitted with transformers, to reduce the voltage, and rectifier circuits, to change the AC into DC (direct current). Direct current always flows round a circuit in the same direction. Devices that run off rechargeable cells or batteries can be charged from the mains and their chargers also contain the same technology - a transformer and a rectifier.

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1. What is DC electricity?
[ ] An electrical source supplying current passing in the same direction
[ ] An electrical source supplying current passing in a constantly changing direction
[ ] An electrical source supplying no current
[ ] An electrical source supplying current passing in the opposite direction to voltage
2. What is AC electricity?
[ ] An electrical source supplying current passing in the same direction
[ ] An electrical source supplying current passing in a constantly changing direction
[ ] An electrical source supplying no current
[ ] An electrical source supplying current passing in the opposite direction to voltage
3. Most electrical devices connect to the mains supply using what connector?
[ ] 3-Pin plug
[ ] 1-Pin plug
[ ] 4-Pin Plug
[ ] 5-Pin Plug
4. In a plug there are three wires. What color is the earth wire?
[ ] Blue
[ ] Green
[ ] Green and yellow
[ ] Brown
5. Why are cables insulated with plastic sheaths?
[ ] For esthetic value
[ ] To protect from electric shock
[ ] To improve the conductivity of the wires
[ ] There is no reason for the cable to be covered
6. Why do plugs contain fuses?
[ ] To protect the device from damage
[ ] To protect from electric shock
[ ] Fuses are not used in electrical devices
[ ] To protect the device from damage and to protect from electric shock
7. Appliances with metal casing are usually what?
[ ] Earthed
[ ] Unearthed
[ ] More expensive than a house
[ ] Live
8. What type of current does a cell or a battery produce?
[ ] DC
[ ] AC
[ ] No current
[ ] Positive current and negative voltage
9. What is the correct formula for calculating the frequency of a supply?
[ ] f = 1T
[ ] f = 12T
[ ] f = 2T
[ ] f = 3T
10. What is the frequency of a supply which has a time period of 100 seconds
[ ] 10 Hz
[ ] 1 Hz
[ ] 0.1 Hz
[ ] 0.01 Hz
Physics: Senior High School: 11th and 12th Grade Quiz - Electricity - Household Electricity (Answers)
1. What is DC electricity?
[x] An electrical source supplying current passing in the same direction
[ ] An electrical source supplying current passing in a constantly changing direction
[ ] An electrical source supplying no current
[ ] An electrical source supplying current passing in the opposite direction to voltage
This can be generated using a dynamo or from chemical reactions that occur inside electrical cells
2. What is AC electricity?
[ ] An electrical source supplying current passing in the same direction
[x] An electrical source supplying current passing in a constantly changing direction
[ ] An electrical source supplying no current
[ ] An electrical source supplying current passing in the opposite direction to voltage
This can be generated using an alternator or by connecting a device known as an inverter to a DC supply. You can buy inverters that can be connected to the cigarette lighter socket of a car which will change the 12 V DC of the battery to 230 V AC so that you can use devices like a phone charger or laptop charger that require mains electricity
3. Most electrical devices connect to the mains supply using what connector?
[x] 3-Pin plug
[ ] 1-Pin plug
[ ] 4-Pin Plug
[ ] 5-Pin Plug
You need to know which color wire goes to what pin - check your knowledge in the next question
4. In a plug there are three wires. What color is the earth wire?
[ ] Blue
[ ] Green
[x] Green and yellow
[ ] Brown
The earth wire is green and yellow, the live wire is brown and the neutral wire is blue
5. Why are cables insulated with plastic sheaths?
[ ] For esthetic value
[x] To protect from electric shock
[ ] To improve the conductivity of the wires
[ ] There is no reason for the cable to be covered
Plastics are flexible and do not conduct electricity
6. Why do plugs contain fuses?
[ ] To protect the device from damage
[ ] To protect from electric shock
[ ] Fuses are not used in electrical devices
[x] To protect the device from damage and to protect from electric shock
When too much current passes through a device the fuse breaks, disconnecting the circuit and so ensuring the device is not damaged and there is no risk of electric shock
7. Appliances with metal casing are usually what?
[x] Earthed
[ ] Unearthed
[ ] More expensive than a house
[ ] Live
An appliance with a metal casing will always have a wire attached to the case which is connected to the earth wire. This means that in the event of a fault with the appliance, it will not cause an electric shock to anyone touching it
8. What type of current does a cell or a battery produce?
[x] DC
[ ] AC
[ ] No current
[ ] Positive current and negative voltage
It has a positive pole and a negative pole
9. What is the correct formula for calculating the frequency of a supply?
[x] f = 1T
[ ] f = 12T
[ ] f = 2T
[ ] f = 3T
Frequency is measured in Hertz (Hz) and the time period is measured in seconds (s)
10. What is the frequency of a supply which has a time period of 100 seconds
[ ] 10 Hz
[ ] 1 Hz
[ ] 0.1 Hz
[x] 0.01 Hz
One divided by one hundred seconds