Physics Paper 3 WASSCE (SC), 2018

Alternative B

 

Question 3B

 

You are provided with an ammeter, a voltmeter, a resistance box, connecting wires, dry cells and other necessary materials.

  1. Measure and record the length XY of the resistance wire provided.
  2. Connect the circuit as shown in the diagram above.
  3. With R = 0Ω, close the key K. Read and record the current, I and the corresponding voltage drop, V across the wire.
  4. Setting R = 1Ω, close the key. Read and record the current, I and the corresponding voltage drop, V across the wire.
  5. Repeat the procedure for five other values of R = 5Ω, 10Ω, 20Ω, 40Ω and 60Ω. Tabulate your readings.
  6. Plot a graph of V on the vertical axis and I on the horizontal axis.
  7. Determine the slope, s, of the graph.
  8. State two precautions taken to ensure accurate results.

 

(b)       (i)       Mention and state the law on which the experiment in 3(a) is based.

 

Observation

 

Part (a) This was a popular question among the candidates. Candidates performance was fair.
(b) Candidates response was fair.

The expected response:

  • Five values of R recorded in ohms
  • Five values of I recorded to at least 1d.p in A and in trend
  • Five values of I-1 correctly evaluated to at least 3 s.f
  • Composite table at least R, I and I-1 
  • Both axes correctly distinguished
  • Plot a graph using reasonable scales
  • Draw line of best fit
  • Determine the slope and intercept of the graph
  • Evaluate 
  • State any two of the following precautions.

e.g.

  • Ensured key opened in between readings/when reading were not taken
  • Ensured tight connections
  • Avoided parallax error when taking reading on ammeter
  • Ensured clean terminals
  • Repeated readings shown on table
  • Noted/Corrected zero error on ammeter

         b(i)         R = 10 Ω correctly shown on graph                                                           
Corresponding value of I-1 correctly read                                                   
I correctly evaluated                                                                                   

         (ii)          Differences between

Shunt

Multiplier

-  Connected parallel to/across the milliammeter

-  Has low resistance

-  Converts milliammeter to an ammeter

-  Connected in series with a milliammeter

-  Has high resistance

-  Converts milliammeter to a voltmeter