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Current Electricity
Charge, current and potential difference
• What is an electric current?• How can we calculate the charge flow in a
circuit?• What are charge carriers?• What do we mean by potential difference?
What is an electric current?
For current to flow you must have a complete circuit
A power source is needed to create a POTENTIAL DIFERENCE
When these conditions are met free electrons move about inside the metal.
Which way does current flow
Current Electrons
The unit of current is the Ampere (A)
The symbol for current is I
The ping pong experiment
Draw the diagram of the ping pong experiment in your book
Explain how the charge carriers (electrons) flow around the circuit.
The unit of charge is the coulomb (C)
The coulomb is defined as equal to the charge flow in one second when the current is one Ampere.
The symbol of charge is Q
∆Q = I ∆t
To calculate the change in charge in a circuit you must multiply the current by the change in time
∆Q = I ∆t1A in 10s is 10C3A in 10s is 30C5A in 200s is 1000C
As the charge of an electron is 1.6 x 10 a current of 1A along the wire must be due to
6.25 x 10 electrons passing per second.
-19
18
e = 1.6 x 10 C-19 Summary questions
The current in a certain wire is 0.35A. Calculate the charge passing a point in the wire 1)In 10 s 2) in 10 minuteCalculate the average current in a wire through which a charge of 15C passes in1) In 10 s 2) in 10 minute
1)
2) Calculate the number of electrons passing a point in the wire in 10min when the current is1) 1.0µA 2) 5.0 A
Basic Electrical Circuits
Calculate the charge of the circuits drawn on the board if they were running for
10 s10 min
∆Q = I ∆t
V = IR
You should know this formula from earlier work
Calculate the resistance of the bulb in the circuits drawn on the board
What is the unit of current?
What is the symbol of current?
What is the unit of charge?
What is the symbol of charge?
What does delta (∆) mean
Write these into sentences in your books
e.g the unit of charge is..... Can you remember without looking?
