Planning Question :November 05 Q1
To investigate how the deflection of a stream of water depends on the electric field strength keeping the flow rate constant.
Diagram :
DC supply to 2 parallel plates clamped with insulated clamps and retort stand . Voltmeter connected across the plates(note : mistake on the diagram for voltmeter) .A stream of water could be supplied from burette connected to water supply.
Procedure :
1 Set up circuit as shown in diagram. Turn on the DC supply keeping the voltage constant . Record the reading of the voltmeter V and measure the distance between the plates d using a ruler.
2. Calculate the electric field strength E using the formula E= V/d
3. Turn off the DC supply and turn on the burette tap . Measure the position of the water stream y1using the traveling microscope scale. Turn on the DC supply and measure the new position of the water stream y2. Turn Off the DC supply.
4. Calculate the deflection y using the formula y = y2-y1.
5. Repeat steps 1 to 4 by varying the distance d to obtain 6 sets of E and y.
6. Plot a graph of lg y vs lgE assuming the equation y = kE*. If the graph is linear the equation is valid and the gradient is * and the intercept c = lg k.
Reliability and precaution :
1 The flow rate is kept constant by ensuring that the water in the burette is always at the same level and the tap fully open.
2. The parallel plate is kept at equidistant apart at the top and the bottom using clamps at the top and bottom of the plates.
3. Voltage of the DC supply is maintained by always checking the voltmeter.
4. Take repeated readings of the traveling microscope scale and obtains the average y.
5. The jet of water should be kept very small so that the point of reference of the stream is easily located when viewed from traveling microscope.
6. Use sufficiently long parallel plates and keep the water stream at the centre between the two plates.
7. The traveling microscope is positioned to measure the same location of the stream of water throughout the experiment.
