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PHYSICS_10_23_V1_P_Ohm's law in complete circuits.pptx
Direct current Ohm's law to complete circuit
Learning objective
To apply Ohm's law to complete
circuit
Assessment criteria
Knowledge
Starter activity: Guess now!
Derive the Ohm’s law to complete circuit
As charge goes around the circuit the sum of EMFs must equal the sum of voltage drops leading to:
ε = I R + I r
The terminal voltage is equal to I R so this can be rearranged to give:
V = ε – I r
and interpreted as terminal voltage = EMF – ‘lost volts’
Energy is conserved. Imagine a unit of charge, Q, moving around the circuit:
Q ε = Q I R + Q I r
This leads to the same equations as in (1) above.
Use Ohm’s law with E ‘driving’ current through the combined resistance (R + r):
I = ε / (R+r) Ohm's law to complete circuit.
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(f) Formative assessment questions
REFLECTION
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