Circuit symbols: Answers
Draw the symbols for the following circuit components: battery, thermistor, variable resistor and fuse.
What are the functions of the following components: diode, fuse and ammeter?
Diode: ensures current travels in one direction only. It can be used to convert alternating current (AC) to direct current (DC).
Fuse: it has a wire running through it which melts if the current becomes too high in the circuit. It is important because it prevents the wire from overheating and causing a fire.
Ammeter: used to measure the current (in amps) in a circuit.
Which component can be used to show the presence of current running through a circuit?
Anything which emits light is useful for showing that a circuit is working (i.e. current is running through the wires). A filament lamp or light-emitting diode (LED) would be suitable.
How are voltmeters and ammeters connected in a circuit?
Voltmeters are connected in parallel (in a side-branch) whereas ammeters are connected in series (in the same loop).
Give some practical uses of light-dependent and temperature-dependent resistors.
Light-dependent resistors are used for sensors and street lighting. Temperature-dependent resistors, or thermistors, are used for thermostats and fire alarms.
Energy and Voltage in Circuits: Answers
Why is domestic lighting connected in parallel?
Lighting in houses and other buildings is connected in parallel because this means that all lights receive the same high levels of voltage (remember that voltage is the same for components connected in parallel but shared between components connected in series). Another advantage is that if one bulb blows, the rest will keep working. If the lights in your house were connected in series, when one bulb stops working then all the lights would go off and you’d have a tricky time trying to figure out which of the bulbs is faulty.
If I replaced the components in a circuit with components of higher resistance, how would this affect the current?
Resistance is defined as how difficult it is for current to move through a circuit. If components with higher resistance are used, it is going to be more difficult for the electrons to move through the circuit and the current decreases.
The current running through a circuit is 10 A. 3 fixed resistors are placed in series, each with a resistance of 5 Ohms. What is the potential difference in the circuit?
Total resistance in the circuit = 3 x 5 = 15 Ohms
Potential difference (voltage) = current x resistance
Potential difference = 10 x 15 = 150 V
A circuit has an ammeter reading of 12 A. How many coulombs of charge pass through the circuit in one hour?
Charge = current x time (in seconds)
Time in seconds = 60 mins x 60 = 3600 seconds
Charge = 12 x 3600 = 43,200 C
How much energy is transferred in a circuit when 1000 coulombs of charge pass through a component with a potential difference of 25 V?
Energy transferred = charge x voltage
Energy transferred = 1000 x 25 = 25,000 J or 25 kJ
What is the difference between AC and DC current?
Alternating current (AC) is where the movement of electrons through the wire constantly reverses its direction. In direct current (DC), the electrons travel in one direction only.