|
|
.gif) |
Click
on the switches to close the circuits.
|
This is a
very simple control system.
Without the
switch we couldn't manually take control. It is very useful to have switches on our walls to control our room lighting. Control switches on our TV remotes allow us to change the channels we are watching, or apps we are using.
How the Circuit
Works
Voltage
The power for
the circuits above, comes from the battery.
Batteries can be low voltage types (1.5 volts) to higher
voltage types (9 volts). High power car batteries are12 volts.
The switch,
when closed, will conduct and let the battery
connect to the rest of the circuit. In this position we say the switch makes the circuit.
The switch,
when opened, will insulate and disconnect the
power source from the rest of the circuit. In this position we say the switch has made an "open circuit"
In our torch circuit
it is important to match the battery voltage
with the correct lamp. This prevents it overloading and getting damaged. This is important for many of the other components we use in electronic circuits.
Current
For the lamp to light up, current needs to flow through it. In a closed circuit: power from the battery flows through the connecting wires, into the lamp and back to the battery.
Current is measured
in Amperes (amps). The smaller currents in electronic circuits are usually measured in milliamps (mA). A milliamp is the same as one thousandth of an amp.
1mA = 1/1000
amp
|
Close
the switch
to
see the current flow from the positive (+) side of the battery
to the negative (-) side.
|
If you had
no lamp and just connected the battery ends
together with wire you would allow a very high current to flow.
|
Click
on the switch to see what would
happen to the wire if there was no lamp and a car battery was
being used.
|
|
Resistance
In the second
circuit, a wire connects the two ends of the battery together. With very little resistance provided by the wire, the current flowing from the battery is very high and the thin wire soon glows redhot and melts. In this situation the battery has been short- circuited.
Although these larger batteries are designed to produce the higher currents demanded by a car, if its terminals are connected together (or shorted), this can make them catch fire or even explode. To prevent damage to a car battery and stop it overheating there are many fuses in a car - each designed to "blow" when the current flowing through it becomes too high.
When the lamp was included (in the first
circuit above), the current was much lower - as the lamp resisted its flow.
Q9, Is this statement true or false ? (you may need to
look back at the Resistance section above).
A "short circuit" across
the contacts of a battery has a very
low resistance - so a lot of current will flow through it.
|
In a circuit
Ohm's
Law
says:
Power
Different electrical
circuits use different amounts of power. A
torch can use quite a lot of battery power and you have
probably found that its batteries need to be replaced more
often than the batteries in a wrist watch. Power is dependent
on the voltage and the current in the circuit. It is measured
in Watts.
Power (Watts)
= Voltage (V) x Current (I)