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NABTEB Basic Electricity Questions And Answers
(a) State the symbol and the numerical meaning of the following:
b. A 400F capacitor is charged by a steady current of 0.4A Flowing for
(i) Calculate the final value of the charge stored in the capacitor
and the p.d between it’s plates.
(ii) If the capacitor is subsequently discharged in 60 micro
Calculate the average discharged current.
(a) Define the following and give TWO examples of each (i) Insulator (ii) Conductor (b) An orange of mass 50g falls from rest from a height of 40m. Calculate the kinetic energy of the orange after falling a distance of 25m. (Neglect air resistance Take g = 10m/S2 ).
(i) An insulator is a material that does not allow electrons to pass through it freely. It is therefore a non-conductor of heat and electricity. Examples are plastic, wood, paper, silk, wool, e.t.c.
(ii) A conductor is a material that allows charges to pass through it freely. It is therefore called conductor of heat and electricity. Examples are metals, the human body, the earth, electrolytes, e.tc.
(a) Describe briefly, with the aid of sketches how an auto transformer differs from a double-wound transformer. (
b) Give ONE advantage and ONE disadvantage of the autotransformer compared with a double-wound transformer
(c) Calculate how many coulombs of electricity flow around a circuit when a current of 10A flows for 30 seconds.
(a) A purely capacitive circuit of 31.8F is connected to a 240V
50HZ supply. Calculate the capacitive reactance and the
(b) List THREE types fluxes and FOUR advantages for using it
is soldering work.
b. Three types of fluxes
(i) Pure amber Resin
(ii) Activated Resin and
(iv) Killed spirit
Four advantages for using fluxes in soldering works
i. It helps to remove oxide film from the surface of the conductor
ii. It helps to prevent the oxide film from re-formation (prevents
iii. Helps to keep the joints wet
iv. Helps as cleaning agent
v. Helps for easy flow of solder over the joints (Any four)
(a) What is a Resistor? Give its symbol
(b) List THREE types of Resistors
(c) Three resistors of values 15, 20 and 30 are connected in
series. If a voltmeter connected across the 20 resistor reads
(i) total resistance of the circuit
(ii) current in the 30 resistor
(iii) Voltage drop in the 15 resistor
(iv) Power consumed by the circuit
(a) Define capacitance and state its unit of measurement
(b) Enumerate FOUR types of capacitors
(c) Three capacitors of values 5f, 15f and 30f are connected in
series. Another capacitor of value 50f is connected in parallel
with the series group across a 200V d.c. source. Calculate.
(i) total capacitance of the series group
(ii) total capacitance of the circuit
(iii) total charge stored in the capacitor
(iv) energy stored by the 50f capacitor
4a. The ability of a capacitor to store electric charges is known as
capacitance. It can also be defined as the ratio of the amount of
electricity (charge), Q transferred from one plate to the other, to the
potential difference produced between the plates. The symbol is C
and it is given as C = Q/V
The unit of measurement of the capacitance is Farad F (coulomb per
4b) Types of Capacitors
(i) Paper capacitor
(ii) Electrolytic capacitor
(iii) Ceramic capacitor
(iv) Silver mica capacitor
(v) Plyester capacitor & poly carbonate capacitor
(vi) Tantalum capacitor
(vii) Polystyrene capacitor
(a) Define the following terms in relation to alternating current and
(i) inductive reactance
(b) A 200f capacitor is connected in series with a 60 resistor.
The combinations is connected to a 200V, 50Hz supply.
(i) capacitive reactance of the capacitor
(ii) inpendance of the circuit
(iv) power factor
a(i) Inductive Reactance is the opposition to alternating current due to the
presence of an inductor in the circuit. It is given as XL and can be
obtained from the relationship that, XL = 2πfL. The symbol is XL and
its unit is ohms.
a(ii) Impedance is the effective or total opposition to alternating current
due to the presence of an inductance coil (an inductor), the capacitor
and a resistor in an A.C. circuit.
The impedance is represented with a symbol Z and its unit is ohms.
a. (i) State ONE application of a capacitor
(ii) Capacitors 8f, 12f and 20f are connected in a circuit
Calculate the resultant capacitance when connected in:
b. State the factors which affect the resistance of a conductor
a. (i) Define electromotive force
(ii) State the unit and symbol of electromotive force
b. A dry cell of emf 3v and an internal resistance of 0.5 is connected to a
load resistance of 7
(i) the load current
(ii) the voltage drop across the internal resistance
a. State the factors which affect the resistance of a conductor
b. Determine the range of resistance of a resistor which has the
following colour codes; Blue, Black Red and Silver
c. Two resistance of values 10 and 20 are connected in parallel
across a 240v battery
(i) The total resistance
(ii) The total current
(iii) The energy consumed in the 12 resistor
a. Factors that affect the resistance of a conductor
The nature of the conductor
The length of the conductor
The cross sectional area of the conductor
The temperature of the conductor
The resistively of the conductor
a. i. Define capacitance
ii. State the THREE factors that determine the capacitance of a
b. Three capacitors of values 6f, 10f and 14f respectively are connected in
series across 10V d.c source. Determine
(i) The total capacitance of the group
(ii) The total charge stored by the capacitors
(iii) The energy stored in the circuit.
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