Definition of e.m.f with regards to energy transfer
e.m.f is measured using a voltmeter connected in parallel with the cell
Definition of potential difference with regards to energy transfer
Although voltage and potential difference are the same thing, make sure not to confuse them with e.m.f, which is slightly different!
Circuit showing the e.m.f and internal resistance of a power supply
e.m.f equation
A battery of e.m.f 7.3 V and internal resistance r of 0.3 Ω is connected in series with a resistor of resistance 9.5 Ω.Determine:
a) The current in the circuit
b) Lost volts from the battery
Aims of the Experiment
The overall aim of the experiment is to investigate the relationship between e.m.f and internal resistance by measuring the variation of current and voltage using a variable resistor
Variables
ε = I (R + r)
ε = IR + Ir = V + Ir
V = –rI + ε
Systematic Errors:
Random Errors:
In an experiment, a student uses a variable resistor as an external load. The current flowing through the circuit is measured with a suitable milliammeter and the potential difference across the variable resistor is measured with a voltmeter for a range of resistance values.The data collected was as follows:Plot a graph of these results and determine the e.m.f. and the internal resistance directly from the graph.
Step 1: Plot the data on a graph of V against I and draw a line of best fit
Step 2: Draw the largest triangle possible in order to calculate the gradient
Step 3: Determine the e.m.f. and the internal resistance from the graph
V = –rI + E
转载自savemyexams
© 2024. All Rights Reserved. 沪ICP备2023009024号-1