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| Questão | Responda |
| What is it meant by direct current and alternating current? | Direct current is in one direction only. Alternating current repeatedly reverses its direction. |
| What do we mean by the peak voltage of an alternating potential difference? | The peak voltage of an alternating potential difference is the maximum voltage measured form zero volts. |
| What do we mean by the live wire and the neutral wire of a mains circuit? | A mains circuit has live wire that is alternately positive and negative every cycle and a neutral wire at zero volts. |
| How do we use an oscilloscope to measure the frequency of an alternating current? | Frequency= 1 ____________________________ time taken for 1 cycle |
| What is the casing of a mains plug or socket made from and why? | Socket and plugs cases are made of stiff plastic materials that enclose the electrical connections. Plastic is used because it is a good insulator. |
| What is in a mains cable? | Mains cable consists of two or three insulated copper wires surrounded by an outer layer of flexible plastic material. |
| What colour are the lives, neutral and earth wires? | The live wire is brown, the neutral wires is blue, and the earth wire is green and yellow. |
| Why does a 3-pin plug include an earth pin? | The earth wire is connected to the longest pin and is used to earth the metal case of a mains appliance. |
| Why is a fuse always on the 'live' side of an appliance? | This cuts the appliance off from the live wire if the fuse blows. |
| What is a circuit breaker? | A circuit breaker is an electromagnetic switch that opens and cuts off the current if too much current passes through the circuit breaker. |
| Why are appliances with plastic cases not earthed? | A mains appliance with a plastic case does not need to earthed because plastic is an insulator and cannot become alive. |
| What is the relationship between power and energy? | The power supplied to a device is the energy transferred to it each second. |
| How can we calculate electrical power and what is its unit? | Electrical power supplied(watts)=current(amperes)*potential difference (volts) |
| How can we calculate the current for a fuse? | Correct rating (in amperes) for a fuse: electrical power (watts) =___________________________ potential difference (volts) |
| What is an electrical current? | An electrical current is the rate of flow of charge. |
| How do you calculate charge from current and time? | Charge (coulombs)=current (amperes)*time(seconds) |
| What can we say about the electrical energy supplied by the battery in a circuit and the electrical transferred to the components? | When charge floes round a circuit for a certain time, the electrical energy supplied by the battery is equal to the electrical energy transferred to all the components in the circuit. |
| Why are electrical faults dangerous? | Because they can cause electric shock and fires. |
| How can we prevent electrical faults? | Never touch a mains appliance with wet hands. Never touch a bare wire or a terminal at a potential of more than 30V. |
| When choosing an electrical appliance, what factors in addition to cost should be considered? | When choosing an electrical appliance, the power and efficiency rating of the appliance need to be considered. |
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