Download ELECTROMOTIVE FORCE AND POTENTIAL DIFFERENCE

ELECTROMOTIVE
FORCE AND
POTENTIAL
DIFFERENCE
EMF
Power stations transfer energy from other forms into electrical
energy
Once this electrical energy has been created it can be used to
power components.
Only capacitors can store electrical energy
Electromotive Force (e.m.f.) is the energy transferred per unit
charge from one type of energy to electrical.
State the definition
of current
Describe the experiment
that discovered the
quantisation of charge
Use Kirchoff’s
First Law
EMF
e.m.f is measured in
It is an expression of the maximum potential difference across
the
1 volt =
Mains electricity (
with
J
V) is therefore supplying each coulomb
Derive the expression for e.m.f.
State the definition
of current
Describe the experiment
that discovered the
quantisation of charge
Use Kirchoff’s
First Law
EMF
e.m.f tells us how much work is done on the charge
State the definition
of current
Describe the experiment
that discovered the
quantisation of charge
Use Kirchoff’s
First Law
POTENTIAL DIFFERENCE
Potential difference is the amount of energy
transferred per unit charge from electrical energy to
another form.
V = W/Q
State the definition
of current
Describe the experiment
that discovered the
quantisation of charge
Use Kirchoff’s
First Law
VOLTS
What are both e.m.f and p.d measured in?
An e.m.f. of 1V means that 1J of energy is transferred to
every Coulomb of charge from the supply (cell, generator).
A p.d. of 1V means that 1J of energy is transferred away
from every Coulomb of charge to a component (buzzer,
lightbulb).
State the definition
of current
Describe the experiment
that discovered the
quantisation of charge
Use Kirchoff’s
First Law
VOLTS
• "emf' is the potential difference across a source of electricity when there is
no current through the source.
• Close the circuit and current will flow but the cell may internally resist the
flow.
• The potential difference seen across the terminals of the source will
therefore be less than the potential difference when there is no current.
State the definition
of current
Describe the experiment
that discovered the
quantisation of charge
Use Kirchoff’s
First Law
KIRCHOFF’S 2nd LAW
By building a simple test circuit compare the e.m.f
and p.d in both series and parallel circuits
A
V
State the definition
of current
Describe the experiment
that discovered the
quantisation of charge
Use Kirchoff’s
First Law
KIRCHOFF’S 2nd LAW
Investigate how current varies with potential
difference in a series circuit with a fixed resistor.
-Draw a results table which includes currents in both
directions
-Plot a graph of p.d. (x) against current (y).
-Calculate the gradient. How does this relate to the
value of resistance of your resistor?
-How are V, I & R related?
State the definition
of current
Describe the experiment
that discovered the
quantisation of charge
Use Kirchoff’s
First Law
KIRCHOFF’S 2nd LAW
Measuring e.m.f. & p.d. in a circuit –
Conclusions:
•Series circuit – e.m.f. is equal to the sum of ….
•Parallel circuit – The e.m.f is equal to the...
State the definition
of current
Describe the experiment
that discovered the
quantisation of charge
Use Kirchoff’s
First Law