Electrical Systems Flashcards
What is a circuit?
A circuit is a system consisting of a power source and a selection of active and passive devices connected together by conductive wires or the tracks on a circuit board allowing the continued flow of current
What is the difference between a DC and an AC? What does DC and AC stand for?
- A power source may be DC (direct current) such as a battery or AC (alternating current) such as mains power
- DC power supplies provide a fixed voltage (e.g. 9 V battery or 1.5 V battery).
- For a DC power supply, we assume that current flows out of the positive terminal, through the circuit and then returns to the negative terminal. This is called conventional current flow.
- AC power supplies provide a sinusoidal supply that varies with time. AC supplies are characterised by the frequency which is the number of complete power cycles each second.
What is Ohms law?
Ohm’s Law: V=IR.
All materials offer some resistance to the flow of current; what is the resistance in conductors and what is the resistance in insulators
All materials offer some resistance to the flow of current
The resistance is very low in conductors
The resistance is very high in insulators.
What offers no resistance to current flow?
Only superconductors when cooled below the critical temperature (which is usually close to absolute zero) offer no resistance to current flow.
What is the different between a parallel circuit and a series circuit?
In a parallel circuit electricity can break off into different paths
In a series circuit if one thing is missing, it all stops
What are Christmas lights often on? What happens when one of the Christmas lights goes out?
Christmas lights are not connected in series (one loop), if one goes out, they all don’t go out
What is resistance?
The resistance of a component is how much it resists the flow of the current
What happens as the resistance gets higher?
The more resistance a circuit has, the harder it is for electricity to flow which reduces the current.
How many bands is a resistor normally have?
Resistors use a colour code to indicate its value.
The code consists of a series of coloured bars.
There may be 3 to 6 colour bars, 4 and 5 band resistors are most common
On a 4 band resistor, what does the band 1 mean, band 2 mean, band 3 mean, band 4 mean?
Band 1: First digit
Band 2: Second digit
Band 3: Multiplier (e.g. 10^2)
Band 4: tolerance in percent
What does LED stand for?
The Light Emitting Diode (LED) is a semiconductor device that can be installed in a circuit as an indicator of activity or power.
Why are LED’s more superior that fluorescent or incandescent lights?
LED’s provide significant advantages over conventional (fluorescent or incandescent) lighting due to an almost limitless colour selection, very low power consumption, low waste heat production and long life.
What does a common LED operate on
A typical LED operates with a forward current of only 20 mA.
What does an LED require to be able to operate?
It is therefore necessary to provide a series resistor to limit the current supplied to the LED.
