DC3 pracs Flashcards
Describe how you would calculate internal resistance.
Set up the circuit with a battery, a variable resistor, an ammeter in series, and a voltmeter across the battery terminals.
Measure the EMF of the battery by setting the circuit to an open circuit (no current flowing).
Adjust the variable resistor to change the current
and record corresponding values of voltage
Plot a graph of V against I
Determine the internal resistance from the graph:
The y-intercept gives the EMF.
The gradient of the straight-line graph :
𝑉 = EMF - Ir is -r, so the internal resistance is the negative gradient.
What would happen to the voltmeter reading if the light intensity decreases?
The resistance will increase, the current in the LDR decreases as I = V/R.
The p.d across the fixed resistor decreases because the current decreases (V=IR, R is fixed).
The p.d across the LDR increases because all the p.d’s must add up to the fixed e.m.f (Newton’s second law).
