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5. Lab Procedure

1. Check up the circuit, where there is the power supply; then
check up the circuit with a testing element  and a galvanometer.
x
2. Switch on the key K .
2
3. After switching button K and moving contact C, move the
1
galvanometer needle to zero position and write down distance l on
x
slidewire.
4. Repeat all the actions, connecting normal Weston's element
 instead of  .
N x
l
5. Determine the unknown EMF on formula    N
x N
l
x
6. Write down the results of experiments in the table.

Date Table

l , mm l  , mm l , mm l  , mm  , V
x x N N x

7. Error of determination of unknown electromotive force 
x
namely depends of errors l and l . (Value of  is very precision,
x N N
so error of  may be neglected), therefore the formula for calculating
N
indirect measurement error is

  l  l 
x N x N
  
  l l
x N x N

6. Test questions

1. What are conditions of direct electric current existence?
2. What's electromotive force?

3. Formulate the definition of EMF.
4. What is the essence of the compensation method?
5. Deduce the calculating formula for EMF determination.

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