Electricity revision for CXC
INSTRUCTIONS
All working must be CLEARLY shown
Use sketches where necessary to support your answers
Silent electronic calculators may be used
Students MUST answer ALL questions in Section A and any THREE in section B
All questions should be answered using standard english
DO NOT TURN THIS PAGE UNTIL YO ARE TOLD TO DO SO
Section A: Short answer questions. Answer ALL TEN questions.
1. Draw a labeled diagram of an atom
2. Define Current and state its symbol and unit
3. Draw the symbol for a battery
4. List two types of resistors
5. What is the formular for voltage in terms of current and resistance?
6. Define direct current
7. What s the difference between Energy and Power?
8. What is the color code of a 2500Ω resistor with 5% tolerance?
9. Define frequency.
10. Give the symbol and unit for charge.
Total 20 mks
Section B: Essay type questions. Answer ANY THREE Questions.
1) (a) Define the terms: (i) Resistivity (ii) Temperature Coefficient of Resistance (4mks)
(b) Name THREE factors which affect the resistance of a metallic conductor. (3mks)
(c) A copper cable 1500 m long, has a cross-sectional area of 25 x 10-6 m2 at 20ºC. The resistivity of copper is 1.7 x 10-8 Ωm.
Calculate the
(i) resistance of the cable (R=ρl/A) (4mks)
(ii) resistance of the cable if the temperature rises from 20ºC to 35ºC and the temperature coefficient of copper is 0.004Ω/ ΩºC. (5mks)
(d) Describe the difference between positive and negative temperature coefficients of materials (4mks)
Total marks 20
2) (a) (i) How does alternating current (a.c) differ from direct current (d.c)? (ii) Name a device which works ONLY on a.c and one which works ONLY on d.c. (3mks)
(b) With respect to an alternating voltage, what is meant by the term ‘period’?
` (2mks)
(c) V
All working must be CLEARLY shown
Use sketches where necessary to support your answers
Silent electronic calculators may be used
Students MUST answer ALL questions in Section A and any THREE in section B
All questions should be answered using standard english
DO NOT TURN THIS PAGE UNTIL YO ARE TOLD TO DO SO
Section A: Short answer questions. Answer ALL TEN questions.
1. Draw a labeled diagram of an atom
2. Define Current and state its symbol and unit
3. Draw the symbol for a battery
4. List two types of resistors
5. What is the formular for voltage in terms of current and resistance?
6. Define direct current
7. What s the difference between Energy and Power?
8. What is the color code of a 2500Ω resistor with 5% tolerance?
9. Define frequency.
10. Give the symbol and unit for charge.
Total 20 mks
Section B: Essay type questions. Answer ANY THREE Questions.
1) (a) Define the terms: (i) Resistivity (ii) Temperature Coefficient of Resistance (4mks)
(b) Name THREE factors which affect the resistance of a metallic conductor. (3mks)
(c) A copper cable 1500 m long, has a cross-sectional area of 25 x 10-6 m2 at 20ºC. The resistivity of copper is 1.7 x 10-8 Ωm.
Calculate the
(i) resistance of the cable (R=ρl/A) (4mks)
(ii) resistance of the cable if the temperature rises from 20ºC to 35ºC and the temperature coefficient of copper is 0.004Ω/ ΩºC. (5mks)
(d) Describe the difference between positive and negative temperature coefficients of materials (4mks)
Total marks 20
2) (a) (i) How does alternating current (a.c) differ from direct current (d.c)? (ii) Name a device which works ONLY on a.c and one which works ONLY on d.c. (3mks)
(b) With respect to an alternating voltage, what is meant by the term ‘period’?
` (2mks)
(c) V