# Problems: Electric circuits

Fill in the missing words:

1. A current is a flow of . . . . . . . . . . . . . . . . . . .
For this to happen there must be a . . . . . . . . . . . . . . . . .
2. Copper is a good . . . . . . . . . . . . . . . . . .
Plastic is an . . . . . . . . . . . . . . . . . .
3. Current is measured in . . . . . . . . . . . . . . . . . using an . . . . . . . . . . . . . . . . . placed in . . . . . . . . . . . . . . . . . in a circuit.
4. Potential difference (p.d.) is measured in . . . . . . . . . . . . . . . . . . using a . . . . . . . . . . . . . . . . . . placed in . . . . . . . . . . . . . . . . . . across a component.
5. Ohm’s Law:
the . . . . . . . . . . . . . . . . . . flowing through a conductor is . . . . . . . . . . . . . . . . . to the . . . . . . . . . . . . . . . . . . difference across it, providing the . . . . . . . . . . . . . . . . . . is constant.
6. The formula connecting V (. . . . . . . . . . . . . . . . difference),  I (. . . . . . . . . . . . .) and R (. . . . . . . . . . . . . . . . .) is :
7. Resistance is measured in . . . . . . . . . . . . . . . . . .
The resistance of a wire increases as the length . . . . . . . . . . . . . . . . .; as the temperature . . . . . . . . . . . . . . . . .  ; and as the cross-sectional area . . . . . . . . . . . . . . . . .

1. Germanium and silicon are called . . . . . . . . . . . . . . . . .
A diode will pass a current only when it is . . . . . . . . . . . . . . . . – biassed.
2. A diode is useful as a half-wave . . . . . . . . . . . . . . . . . . to convert . . . . . . . . . . . . . . . . . . current to . . . . . . . . . . . . . . . . . current.
The output can be smoothed by a . . . . . . . . . . . . . . . . . . .
3. A LED (. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ) is a transducer; it changes . . . . . . . . . . . . . . . . . . energy to . . . . . . . . . . . . . . . . . . energy.
4. When an LDR (. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .) is illuminated, its resistance . . . . . . . . . . . . . . . . . .
When a thermistor is heated, its resistance . . . . . . . . . . . . . . . . .
5. A . . . . . . . . . . . . . . . . . . . . . . . (NO) reed switch does not pass a current until a . . . . . . . . . . . . . . . . . . is brought near it.
6. A . . . . . . . . . . . . . . . . . . current in the coil of a relay can switch on or off a . . . . . . . . . . . . . . . . . current through the contacts.
7. A transistor is used to . . . . . . . . . . . . . . . . . . small currents.
A small current in the . . . . . . . . . . . . . . . . . . circuit causes a . . . . . . . . . . . . . . . . . . current to flow in the . . . . . . . . . . . . . . . . . . circuit.