Transcript Current, voltage and resistance

Current, voltage and resistance
Revise the following:
•
•
•
•
Circuit symbols
Circuit diagrams
Current and voltage in series circuits
Current and voltage in parallel circuits
Circuit symbols
Current, voltage and resistance
• Current = the rate of flow of electrons in a
circuit
• Voltage/potential difference = the
difference in electrical potential energy
between two points in a circuit.
Potential difference is also called voltage
• Resistance = a measure of how hard it is for
electrons to move in an electrical circuit.
Current in a series circuit
In a series circuit, the current flows through
one continuous pathway so the current is the
same in all parts of a series circuit.
1A
A
A
A
1A
1A
Voltage in a series circuit
In a series circuit, the voltage supplied by the battery is shared by
the components so the sum of the potential difference across the
components equals the battery voltage.
V
V
3V
6V
V
3V
As more bulbs are added in series, each bulb has less
potential difference and so the bulbs become dimmer.
Current in a parallel circuit
In a parallel circuit, the current divides at the point where the
circuit branches and then recombines to complete the circuit so
the current is not the same in all parts of a parallel circuit.
2A
A
A
1A
A
A
1A
2A
Voltage in parallel circuits
• In a parallel circuit, the
potential difference across
each bulb is the same as the
potential difference across
the battery.
V
V
6V
6V
• This means that all the
bulbs have the same
brightness, and they are
brighter than the same
number of bulbs in a series
circuit.
• This also means that the
battery will run down faster in a
parallel circuit.
V
6V
Georg Ohm (Ohm’s Law)
• Resistance is a measure of how hard it
is for electrons to move in an electrical
circuit.
• In 1827 a German physics and maths
teacher Georg Ohm discovered a
connection between current, voltage and
resistance
• It was such an important discovery in electricity that the
unit of resistance is called the ohm.
• The formula used to calculate Resistance is called Ohm’s
Law
• This unit is represented by the symbol Ω.
What is the formula/equation for Ohm’s law?
Ohm’s law is usually written as:
voltage = current x resistance
V
=
I x R
This formula can also be written as:
resistance = voltage
current
R
 Voltage is measured in volts (V).
 Current is measured in amps (A).
 Resistance is measured in ohms ().
=
V
I
Current-voltage graphs
A resistor at constant
temperature
Potential difference is
directly proportional to
current.
As pd/voltage doubles,
current doubles
As pd/voltage triples,
current triples
Filament lamp
A smooth
curved line
which levels
off
Diode
No current when
pd/voltage is negative.
When pd/voltage reaches
a certain positive voltage,
current increases and is
directly proportional to
pd
Resistance...