Circuits: Current and Charge
Electrical Analogy, Current and Charge
An electrical Circuit is like a hot water system.
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Circuits: Current and Charge
Analogy
Electrical
Is like the….. Because….
Component
Battery
………
It supplies
……… to the
circuit.
Charge
(electrons)
………
It ……. around
the circuit and
carries ……..
Wire
………
………
It carries the
……../…….
Lamp
……….
It transfers
…….. from the
circuit to the
surrounding
………..
difference in
the water
(before and
after the
heater)
This is a
measure of the
energy
transferred.
A* mark”
Potential
difference
in the
circuit
(across the
lamp)
2
(any short comings
in the analogy)
Water will leak
from a broken pipe,
but electrons will
not ‘leak’ from a
broken wire
Circuits: Current and Charge
Charge
What is the relationship between charge and current?
Definition: Current is the rate of flow of charge.
Current = Charge / time
Current I is measured in Amps A.
Charge Q is measured in Coulombs C.
Time t is measured in seconds s.
Practice Question
Q1. A bucket can hold 12kg of water. A tap starts
fill the bucket at a flow rate of 0.10kg/s. Calculate
time taken to fill the bucket.
to
the
120 seconds which is 2 minutes. 12kg/0.10kg/
s=120 seconds.
Q2. A battery delivers a current of 1.2A to a circuit. After 2.0mins how
much charge has moved around the circuit?
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Circuits: Current and Charge
Electrical Symbols
Identify these common symbols used in circuits.
conductor
resistor
cell
battery
positive battery
A
variable resistor
V
ammeter
lamp
voltmeter
switch open
DC power suply
switch closed
Fuse
??
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Circuits: Current and Charge
Electrical Basics
We need to define some basic properties in electricity:
Charge
The unit of Charge is the Coulomb .
The symbol for charge is Q.
The symbol for the Coulomb is C.
Current
Current is the rate of flow of electric charge .
Current is measured using an Ampere Meter .
A
The unit of Current is the ampere , or coulomb per
second.
The symbol for Current is I.
The symbol for the Amp is A.
Potential Difference
(Potential Difference is the power that makes charge move.)
Potential Difference is the force supplied to the charges
Potential Difference is measured using a volt meter
The unit of Potential Difference is the Joule per Coulomb..
The symbol for Potential Difference is delta V .
The symbol for the Volt is V .
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V
Circuits: Current and Charge
Resistance
Resistance resists the flow of charge and power of the current.
Resistance is calculated from Potential Difference and Current.
The unit of Resistance is the ohm .
The symbol for Resistance is Ω .
The symbol for the Ohm is Ω .
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