Physics Paper 3 WASSCE (SC), 2021

Alternative B

 

Question 3B

 

You are provided with a battery, an ammeter, a voltmeter, a resistance box, a key and connecting wires.

  1. Set up the circuit as shown in the diagram above.
  2. With the key opened, measure and record the e.m.f EO of the battery.
  3. With the key closed, select the resistance R = 1 ῼ on the resistance box. Read and record the current, I.
  4. Evaluate I-1.
  5. Repeat the procedure for five other values of R = 2 ῼ, 3ῼ, 4ῼ, 5 ῼ , and 6ῼ.

In each case, record I and evaluate I-1.

  1. Tabulate the results.
  2. Plot a graph with R n the vertical axis and I-1 on the horizontal axis.
  3. Determine the slope, s, of the graph,.
  4. State two precautions taken to ensure accurate results.

(b)        (i)         Define potential difference in an electric field.
(ii)        A piece of resistance wire of diameter 0.2 mm and length 25 cm has a resistance of 7 ῼ.
Calculate the resistivity of the wire. {]

 

Observation

 

Part (a) Candidates performance was fair. Many candidates attempted this question and the response was fair.
Part (b) Candidates response was satisfactory.

The expected response:

3 (a) OBSERVATIONS

  1. Eo correctly measured and recorded to at least 1 d.p in volts.                          
  2. Six values of R correctly recorded in Ω.                                                            
  3. Six values of I correctly read and recorded to at least 1 d.p in A and in trend. 

Trend: As R increases, I decreases.

  1. Six values of I-1 correctly evaluated to at least 3 d.p                                        
  2. Composite table showing at least R, I and I-1.                                                      

 

GRAPH

  1. Both axes correctly distinguished                                                
  2. Reasonable scales                                                                        
  3. Six points correctly plotted                                             
  4. Line of best fit.                                                                                                    

SLOPE

  1. Large right – angled triangle                                                                                
  2. correctly determined                                                                                      
  3. ∆ I-1 correctly determined                                                                                    
  4.   correctly evaluated  

                                                                             
INTERCEPT
Intercept C on the vertical axis
Correctly shown                                                                                                              
Correctly read

ACCURACY
Based on slope, s, = Eo ± 10 %

PRECAUTIONS
- Ensured clean terminals.
- Ensured tight terminals/connections.
- Opened key when reading was not taken.
- Avoided parallax error on ammeter.
- Zero error noted/corrected/avoided on ammeter.
- Repeated readings shown on table.

b. (i) Potential Difference in an electric field
It is the work done per coulomb in moving a charge between two points.
O R
It is the energy per coulomb released when electricity moves from one point to the other.
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(ii)  ρ                                     
 = = 8.8x10-7