1. Electromotive Force
and Circuit
Tuto, Courtlane B.
Go, Alexandra Jayle D.
Mofar, Marc Raven
Haranay, Juliana B.
Olmido, James Ryan
Quiling, Kiara March
Madjos, Seigfred
2. What is Electromotive Force?
Electromotive force is defined as the
electric potential produced by either
an electrochemical cell or by changing
the magnetic field. EMF is the
commonly used acronym for
electromotive force.
3. Electric Potential
the amount of work needed to move a
unit charge from a reference point to
a specific point against an electric
field
4. Electromagnetic Cell
an apparatus that is used to generate
electricity from a spontaneous
oxidation-reduction reaction, or that
uses electricity to drive a
nonspontaneous reaction.
5. ,
A generator or a battery is used for the
conversion of energy from one form to
another. In these devices, one terminal
becomes positively charged while the
other becomes negatively charged.
Therefore, an electromotive force is a
work done on a unit electric charge.
The electromotive force symbol is “ε”.
6. Following is the formula for electromotive force:
ε = V + Ir
V is the voltage of the cell
I is the current across the circuit
r is the internal resistance of the cell
ε is the electromotive force
7. The Formula for Calculating the EMF
There are two main equations used to calculate
EMF. The fundamental definition is the number of
joules of energy each coulomb of charge picks up
as it passes through the cell.
ε = E/Q
ε electromotive force
E the energy in the circuit
Q Charge of the circuit.
8. We may use the definition more like the
Ohm’s law i.e V = IR. So the formula is,
ε = V + Ir
- V is the voltage of the cell
- I is the current across the circuit
- r is the internal resistance of the cell
- ε is the electromotive force
- This shows that we can calculate the EMF if we know
the voltage across the terminals, the current flowing
and the internal resistance of the cell.
9. Examples for EMF Formula
Consider that we have a circuit with a
potential difference of 3.2 V, with a
current of 0.6 A. The internal
resistance of the battery at 0.5 ohms.
Use EMF
10. .
Solution: Given,
V = 3.2 V
I = 0.6 A
r = 0.5 ohm
Using the formula: ε= V + Ir
ε=3.2+0.6×0.5
= 3.2 V + 0.3 V
= 3.5 V
So the EMF of the circuit is 3.5 V.
11. Find the terminal potential difference of a cell when it is
connected to a 9-ohm load with cell emf = 2 Volts and
resistance (internal) 1 ohm?
emf = 2
External resistance = 9 ohm
Internal resistance = 1 ohm
Since, I = V/R
And R = External resistance + Internal resistance = 9 + 1 = 10 Ohm
Now, I = 2/10 = 0.2 Ampere
12. .
e = V + Ir
2= V+ (0.2)1
V = 2-0.2
Therefore, the external resistor gets,
V = 1.8 Volts.
13. .
The electromotive force (EMF) is
significant since it helps in
determining the amount and
magnitude of energy. This is the
amount of energy involved in the
current passing through the circuit.
