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Direct Current (Electromotive force (emf) (There are 3 emf equations to…
Direct Current
Electromotive force (emf)
efm is the work done per unit charge of a cell.
How do you measure emf?
It is the pd across the terminals of a cell when no current is flowing, so place a voltmeter across the terminals of a cell.
What's the equation?
Because emf is measured in
volts
you can use these equations.
There are 3 emf equations to learn as they are SENT DOWN FROM HEAVEN, OMG THEY WILL SAVE YOUR SOUL IN THE EXAM -so PLEASE learn these!
e = V + v
V = e -Ir
(you will be given this one) e = I(R+r)
What are the circuit rules?
The 3 rules for parallel circuits
The total
current
is the same as the current before it splits into the branches, and the current supplied to each component may be different.
The
potential difference
flowing through each component is the same.
The 3 rules for series circuit
The
current
is the same all around the circuit, and the current supplied to each component is the same.
The
potential difference
is split between components, so more bulbs in series would be dimmer.
Rules that will help you out SO MUCH in the exam
Kirchhoff's 2 laws
The total emf is equal to the sum of potential drops around a loop, (for any complete loop).
Current entering a junction is the same as the current leaving a junction.
The potential divider
.
