Answer Practice 1
1. Answer: B
2. Answer: C
3. Answer: B
4. (a) i) How much work is done when a force of 800.0 N is exerted while pushing a crate across a level
floor for a distance of 1.5 m? (Work = force x distance).
Answer:
Work = Fd, where F = 800N and d = 1.5 m
800 x 1.5 = 1200 Joule
ii) What is the kinetic energy of a 30-gram bullet that is traveling at 200 m/s?
(Kinetic energy = 1/2mv2)
Answer:
KE = 1/2mv2, where m= 3.0 x 10-2 and v = 200
KE = ½ (3.0 x 10-2)(200)2
= 6.0 x 102 Joule
iii) (b) Describe any TWO (2) process of electrification.
(Friction, Contact, Induction)
Answer:
Friction - occurs when two surfaces are rubbed together. Example, a positive charge was created by
rubbing glass with silk and a negative charge was created by rubbing rubber with fur.
Contact/Conduction - means that the charging rod actually touches the electroscope’s knob. Since there
is contact, electrons from the knob would flow onto a positive rod or off of a negative rod. Charging by
conduction leaves the electroscope with a residual charge IDENTICAL to that of the charging rod.
Induction - means that the charging rod is brought close to the electroscope’s knob but NEVER touches
it. If the electroscope is not grounded, it will remain neutral but be temporarily polarized while the
charging rod is in the immediate vicinity. That is, a positive rod will induce the electrons in the scope to
migrate to the knob. This redistribution of charge will result in the leaves of the scope being positively
charged. If the electroscope is grounded during induction, electrons will flow from the knob to the
ground if the charging rod is NEGATIVE and electrons will flow onto the knob if the charging rod is
POSITIVE. The net effect once the grounding wire is removed is that the electroscope will be left with a
residual charge that is OPPOSITE to that of the charging rod.
5. (a) With reference to variable resistors:
i) Define variable resistor (1 mark)
Answer: Variable resistor is a component whose value can be altered either manually or mechanically.
ii) State another name for variable resistors (1 mark)
Answer: Rheostat
iii) Draw the symbol representing variable resistors (1 mark)
Answer:
iv) List any TWO (2) factors affecting resistance (2 marks)
Answer:
Temperature
Length
Material Conductor
Cross sectional area
(b) With reference to capacitors:
i) List the similarities between capacitor charging and discharging (2 marks)
Answer:
 The current flow follows a similar pattern of decay.
 Time constant, T = RC
ii) List the differences between capacitor charging and discharging (2 marks)
Answer:
 Potential difference (PD) rises when the capacitor charges
 Potential difference (PD) falls when the capacitor discharges
iii) What does the term leakage mean in relation to capacitor (1 mark)
Answer: Any capacitor, if left long enough will slowly lose its charge because the dielectric material
between its plates is not a perfect insulator. This is called leakage.