If there is inclination between the search coil and the wire, there will be a component of
the magnetic field formed. The horizontal component of the magnetic field will be
measured. This is not the maximum magnetic field that we want.
8 Why the sensitivity of the search coil can be increased by increasing the frequency?
The more frequent the voltage across the wire, the more frequent is the change of the
magnetic field. The magnetic field across the search coil is proportional to the sensitivity.
9 Tabulate the length l of vertical trace on CRO and current I measured in the table below:
10 Plot a graph of l against I.
11 The length of the vertical trace is directly proportional to the magnetic field of the straight wire. How does the magnetic field vary with the current?
The greater the current, the greater is the magnetic field.
12 Tabulate the length l of vertical trace on CRO and distance r measured in the table below:
13 Plot suitable graph(s) to find out how the magnetic field varies with the distance from the wire.
14 How does the magnetic field vary with the distance from the wire?
The magnetic field is inversely proportional to magnetic field.
15 Check if they agree with the prediction by the formula .
The magnetic field is proportional to the length of the trace in the CRO.
=>=> ( length )( r ) = constant.
Putting the length = 6 , 3.6 , 2.4 , 1.8 , 1.5 , 1.2 , 0.8 and distance = 1 , 2 , 3 , 4 , 5 , 6 , 7
respectively, the constant will found to be around 7.2 .Since different sets of the result are
more or less the same, they agree with the prediction by .
Source of error:
- The search coil may not be the level of the wire.
- There are some other electric wires in the room which can produce changing magnetic field.
- Try to carry out the experiment in a room with fewer or no electric wires.
- Move the search coil to ensure the maximum voltage is recorded.
The magnetic field is directly proportional to current I and inversely proportional to distance r from the wire
Practical Physics for TAS (third edition), Oxford Press, 2005.
A-Level Practical Physics (Third Edition) ©