| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.61 |
| Score | 0% | 72% |
The valence shell of a semiconductor is how full of electrons?
empty |
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less than half full |
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half full |
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more than half full |
Semiconductors have valence shells that are exacly half full and can conduct electricity under some conditions but not others. This property makes them useful for the control of electrical current.
Current is the rate of flow of electrons per unit time and is measured in:
coulombs |
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volts |
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ohms |
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amperes |
Current is the rate of flow of electrons per unit time and is measured in amperes (A). A coulomb (C) is the quantity of electricity conveyed in one second by a current of one ampere.
Alternating current changes __________ many times each second.
period |
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resistance |
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frequency |
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direction |
In contrast to the constant one-way flow of direct current, alternating current changes direction many times each second. Electricity is delivered from power stations to customers as AC because it provides a more efficient way to transport electricity over long distances.
Why does current in an electric circuit create heat?
heat is created when the current overcomes resistance in the wire |
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the wire in the circuit burns when current passes through |
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current is naturally hot |
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voltage is naturally hot |
Current in an electric circuit creates heat when the current overcomes resistance in the wire.
Which of the following statements about a capacitor is false?
to discharge a capacitor safely, use a high-wattage resistor comparable to the capacitance of the capacitor |
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it is safe to touch a capacitor with your hands as long as it is small |
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a capacitor remains charged even after the input voltage is removed |
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you should always discharge any capacitors before working on an electronic circuit |
The purpose of a capacitor is to retain electric charge and it will do so even after its input voltage is removed. After the input voltage is removed, the capacitor will slowly discharge but, depending on the size and characteristics of the capacitor, discharging could take from a few minutes to a few years. So, it's never safe to touch a capacitor with your hands and you should make sure to discharge any capacitors in a circuit before working on it using an appropriately high-wattage resistor or a capacitor discharge tool.