P
- The description of magnetic flux posed some problem to candidates who failed
to see it as basically a collection of (imaginary) lines of force in a magnetic field.
- This part called for a sketch of a given magnetic field. It was poorly reacted to by candidates. Some sketches were rough while some did not indicate the correct direction of the arrows on the magnetic lines.
- Most candidates were able to state ways in which magnetic field is important to life on earth. Performance was fairly alright.
- Listing of applications of electromagnets was well answered by virtually all the respondent candidates. Performance was good.
- The numerical part was poorly tacked most respondent candidates mishandled the standby mode part of the question. Performance was poor.
The expected responses are:
(a) Magnetic flux consists of lines which represent the direction and strength of a magnetic field at any point in the field.
(b)
correct shape of lines of force
correct arrows / directions
two neutral points P correctly indicated
(c) Importance of earth’s magnetic field to life on earth
e.g
- Navigation by sailors and pilots
- Plotting of contour lines by surveyors
- shielding of dangerous radiations / cosmic rays from the sun
(d) Application of electromagnetic
e.g
- loud speakers
- door bells
- automatic switches / relays
- separation of magnetic materials from non magnetic materials
- lifting of heavy magnetic materials
e)
Appliance |
Quantity |
Power rating / W |
Standby power / W |
Total Watt |
KW |
KWh |
Ceiling fan |
3 |
80 |
- |
240 |
0.24 |
1.44 |
Air conditional |
1 |
1500 |
- |
1500 |
1.50 |
1.50 |
Lamps |
7 |
40 |
- |
280 |
0.28 |
2.80 |
Home theatre |
1 |
100 |
5 |
100 5 |
0.100 0.005 |
0.5 0.095 |
Television set |
1 |
80 |
4 |
80 4 |
0.080 0.004 |
0.4 0.076 |
|
14.311 |
NOTE: Standby mode was for 19 hours
- Energy consumed in a day = 14.311 kWh
Energy consumed in 30 days = 14.311 x 30
= 429.33 kWh
(ii) Cost of operating for 30 days
1 KWh N10.00
429.33KWh 429.33 x 10
= N 4293.30
