Questions on electricity are not usually popular among candidates due to insufficient and malfunctioning apparatus. However, this one was attempted by many candidates and their performance was fair.
Many responding candidates failed to record the value of Io as demanded for in the question.
Few candidates confused Ɩ with Ii hence were calculating Ii-1 instead of L-1.
In part (a), candidates were required among other things, to:
- Read and record to at least 1 decimal place the value of ammeter reading ;
- Read and record to 1 decimal place five values of Ii ;
[Trend: L increases as I decreases]
(iii) Evaluate and record to at least 3 decimal places five values of L-1 correctly;
(iv) Record data in composite table showing Ɩ, I and I-1
(v) Correctly distinguish the graph axes, select reasonable scales, plot five points correctly and draw line of best fit;
(vi) State any two of the following precautions in acceptable forms:
- Ensured tight connections/cleaned terminals
- Key removed after each reading
- Parallax error avoided in reading ammeter
- Avoided sliding jockey on potentiometer wire
- Repeated readings shown in table.
(b)(i) E.m.f. is the total work done in pushing one coulomb of electricity round an external resistor and the internal resistor of the source or the total energy obtained per coulomb from a cell or battery.
In part (b) (i) candidates’ responses were poor. In (b)(ii), most candidates could not give the correct formula.
The expected responses were as follows:
(b)(ii) Ey = ly
Ex lx
Ey = 60
1.00 40
Ey = 60 x 1. 00
40
Ey = 1.50V.
Evaluate I0 .