P2 Current and Circuit Symbols (page 179) Flashcards
What is an Electric Current?
It is a flow of electrical charge.
Why can an Electrical charge only flow around a complete (closed) circuit if there is a potential difference?
A current can only flow if there’s a source of potential difference.
What is the unit of a current called?
its called the ‘Ampere (A).
Look at diagram 1 on page 179,
In a single, closed loop (like the diagram), do the current have the same value everywhere in the circuit?
Yes it has the same value everywhere in the circuit (see page 183).
What is Potential difference?
also know as voltage is the driving force that pushes the charge round. Its unit is the volt, V
What do Resistance mean regarding an electrical current flow?
resistance is anything that slows the flow down. the unit is ohm (look at symbol on page 179).
What do the current flowing through a component depend on?
it depends on the potential difference across it and the resistance of the component (see page 180).
The greater the resistance across a component, the smaller the current that flows (for a given potenital difference across the component).
The total charge through a circuit depends on what?
on current and time
What is the size of a Current?
it is the rate of flow of charge.
When Current flows past a point in a circuit for a length of time then the charge that has passed is given by a formula, what is the formula?
Q = It
(Q means charge flow (coulombs, C)
(I means Current (A))
(t means Time (s)) see diagram 2 on page 179).
More Charge passes around the circuit when a larger current flows.
A battery charger passes a current of 2.0 A through a cell over a period of 2.5 hours. How much charge is transferred to the cell?
Q = It = 2.0 x (2.5 x 60 x 60)
= 18 000 C
You need to learn and understand circuit diagrams and draw them using the corect symbols, what do you need to know regarding all the symbols when you draw them?
Make sure all the wires in your circuit are STRAIGHT LINES and the the circuit is CLOSED.
i.e. you can follow a wire from one end of the power supply, through any components, to the other end of the supply (ignoring any switches).
You need to be able to draw and understand:
Cell
Battery
Switch open
Switch closed
Filament lamp (or bulb)
Fuse
LED
Resistor
Variable resistor
Ammeter
Voltmeter
Diode
LDR
Thermistor
see diagram and symbols on page 179.
A laptop charger passes a current of 8 A through a laptop battery. Calculate, in minutes, how long the charger needs to be connected to the battery for 28 8000 C of charge to be transferred (4 marks)?
Q = it so t = Q ÷ I (1 mark)
= 28 800 ÷ 8 (1 mark)
= 3600 s (1 mark)
t = 3600 ÷ 60 = 60 minutes (1 mark)
A student creates a simple circuit containing a battery, a switch and a bulb. He connects them all in a single, closed loop. Draw the circuit diagram for this circuit (3 marks)
look at answer diagram on page 246, p.179, Q2.
1 mark for each correct symbol connected in a single loop, otherwise, award 2 marks for correct symbols in an incorrect loop).
