How can we measure potential difference or emf?
Generally a volt meter is used to measure potential difference or emf
across an electric device like battery. It must be connected in parallel to
the electric device to measure the potential difference across the ends of
the electric device.
When a battery in a torch is used for several weeks, the light from its
bulb becomes dim. We say that the battery or cell in the torch is discharged.
What does it mean?
Is there any relation between emf of battery and drift speed of electrons
in the conductor connected to a battery?
Ohm's law
lab activity
Aim:To show that the ratio V/I is a constant for a conductor.
Materials required: 5 dry cells of 1.5V each, conducting wires,an
ammeter, a volt meter, thin iron/manganin spoke of length 10cm, LED and key.
Procedure: Connect a circuit as shown in fig.-
10. Solder the
conducting wires to the ends of the
iron spoke. Close the key. Note the
readings of
current from ammeter and potential difference from
volt meter
in table 1.
Table:1
Sl no.
potential difference(V)
Current(I)
v/1
Now connect two cells (in series) instead of one cell in the circuit.
Note the respective readings of the ammeter and volt meter and record the
values in table 1. Repeat the same for three cells, four cells and five cells
respectively. Record the values of potential difference (V) and current (I)
corresponding to each case in the table 1. Find V/
I for each set of values.
What do you notice? The ratio V/
I is a constant. We can write this
mathematically as
ammeter, a volt meter, thin iron/manganin spoke of length 10cm, LED and key.