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Welcome! Here are the details for experiment
 
Category : By : Rifaqat Ali Minhas  
Experiment's Objective: In this experiment, you will investigate the resistance of a filament lamp.
Description:
When you are performing this experiment, your values of potential difference should not be greater than 4 V, and you have to give your measured value up to one decimal place. Likewise, the value of electric current should not be greater than 1A, and you have to give your measured value up to one decimal place. You should not forget to complete the column headings of the data table and the value of R should be calculated correctly.
 
Apparatus:
Potentiometer (constantan wire stretched on a meter rule), Voltmeter, Ammeter, six connecting wires with crocodile clips, two battery cells (1.5 V each), two battery boxes (to connect two battery cells in series), switch (It is optional, if you are not using the switch even then you can make direct connection)
 
Procedure:

Carry out the following instructions, referring to Fig. below. The circuit is set up for you.

(a)

  • Switch on. Place the sliding contact C on the resistance wire at a distance d = 0.200 m from point A.
  • Measure and record in Table, the current I in the circuit and the p.d. V across the lamp L. Switch off.
  • Calculate the resistance R of the lamp filament, using the equation R = V / I
  • Repeat the procedure using values for d of 0.400 m, 0.600 m and 0.800 m.
  • Complete the column headings in the table.

DataTable

d/ V/ I/ R/
0.200                         
0.400      
0.600      
0.800      

(b) A student suggests that the resistance R of the lamp filament should be constant.

State and explain whether your results show that R is constant within the limits of experimental accuracy.

statement ..................................................................................................................................

explanation ...............................................................................................................................

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...................................................................................................................................................

[2]

Answer: 

Statement: "No"

Explanation: There is big difference in the values of "R" calculated in the table, so they are not equal within the limit of experimental accuracy.

(c) Suggest, referring to a practical observation, a reason why the resistance R may not be constant in this experiment.

 

...................................................................................................................................................

...................................................................................................................................................

.............................................................................................................................................. [2]

Answer: When electric current passes through the lamp, its temperature changes. So resistance of the lamp changes that is why we are not able to get constant resistant.

(d) (i) Name an electrical component that could be used, in place of the resistance wire AB and sliding contact, to vary the current I.

 

.............................................................................................................................................. [1]

Answer: Rheostate (Any variable resistor)

(ii) Draw a diagram of the circuit including this component in place of the resistance wire and sliding contact.

 
Precautions:

Switch off the circuit between the readings.

 
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