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31 Cards in this Set
- Front
- Back
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What is the name for the rate of flow of charge? |
Current
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How do we calculate the flow of electric charge from the current?
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Charge (c) = current (A) x time (sec)
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What is direct current? |
Current that flows in one direction
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What is the peak voltage of an alternating potential difference? |
The maximum voltage measured from zero volts (for mains electricity the voltage is between 230 to 240 volts)
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Why don't appliances with plastic cases need to be earthed? |
Plastic is an insulator so it cannot become live.
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What energy transfer takes place when charge flows through a resistor? |
The energy transferred makes the resister warm so energy is transferred to the surroundings by both bulb and resistor. |
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why are electrical faults dangerous?
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shocks or electrocution occurs when too much current passes through a wire |
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What is the relationship between power and energy? |
Power = energy / time |
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What is the voltage across the live wire?
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325 volts
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What are the colours of the live, neutral, and earthed wire?
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live- brown
neutral- blue earth- green/yellow |
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What is the advantage of a cuircuit breaker over a fuse? |
cuircuit breakers are
1) easy to reset 2) react very quickly |
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What is the frequency of the UK mains electricity?
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50 hertz
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What variable is on the y-axis on a oscilloscope?
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The voltage. You count the number of square multiply it by value for each square
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What variable is on the x-axis on a oscilloscope?
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The time. Count # of squares multiply it by the value for each square.
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How is the frequency of a wave related to the period?
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frequency (Hertz) = 1 / period (seconds)
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What are the two formulas for electrical power? |
power (watts) = energy (joules) / time (sec)
Power (watts) = potential difference (volts) * current (amps) |
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Define frequency? |
frequency is the number of complete cycles a wave makes in one second.
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How do you use an oscilloscope to measure the frequency of an alternating current? |
Measure the period (time to go one wave). frequency = 1/ period
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Given formula P = I x V
What does I = ? What does V = ? |
I = P/V
V = P / I |
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How do you pick the right fuse?
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Calculate the current using either I = V / R or I = P / V then pick the fuse size that is one bigger than the value calculated.
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What is the casing of a mains socket made from and why?
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They are made of stiff plastic materials that enclose the electrical connections. It is food because it is an electrical insulator.
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Why does earthing a device make it safer? |
Earthing makes sure that no charge can build up on the metal casing. Thus preventing electrocution when you touch it.
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Why does a plastic device (NON METAL CASING) not need a earth wire? |
Plastic is an insulator so no charge can build up thus prevent electrocution.
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Why does a device stop working if there is too much current for the fuse?
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Too much current blows fuse
Blown fuse makes circuit incomplete |
