CP3 EMF and Internal Resistance Flashcards
Graph?
V on the y-axis and I on the x-axis
the gradient is -r and the emf is the y-intersect
How?
Make a circuit with a variable resistor and ammeter in series and a voltmeter in parallel with the cell.
Vary the V and I with variable resistor
How to lower the uncertainty?
Use a new cell with a higher EMF
Keep the temperature constant by opening the switch (or resistance varies)
Check for zero errors
Use of a multimeter as it can be difficult to read meters simultaneously
Why may the determined EMF value be different from real eMF
An ideal voltmeter has infinite resistance, but they don’t.
Why is it safe to use high-voltage supplies?
They have a high internal resistance so the p.d acts on the internal resistor instead of on the low resistance of a human.
Why shouldn’t a rechargeable battery be used?
Very low internal resistance so will make getting values difficult
Hazards?
Hot resistors
Why doesn’t it matter whether the voltmeter is connected across the R or the cell?
As the resistance of an ammeter is meagre, so very little p.d across it,
What might make the value for the emf differ from the true value?
The resistance of the voltmeter isn’t infinite
Small current will cause a p.d across the internal resistance
