**NABTEB BASIC ELECTRICITY OBJ
01-10: DACBDAAADA
11-20: BCBBBCBAAB
21-30: ACBBCBABDC
31-40: DBDDCACAAB**

**COMPLETED**

NABTEB 2024 BASIC ELECTRICITY ANSWERS

ANSWER FIVE QUESTIONS ONLY

(1a)

The purpose of colouring carbon resistors is to indicate their resistance value through a colour code system.

(1b)

(i) Brown Yellow Red and Gold

Brown = 1, Yellow = 4, Red = Multiplier (10²), Gold = ±5%

Resistance value = 14 x 10²

= 1400Ω

Maximum value = 1400 x 1.05

= 1470Ω

Minimum value: 1400 x 0.95

= 1330Ω

(ii) Red Black Green and Silver

Red = 2, Black = 0, Green = Multiplier (10⁵), Silver = ±10%

Resistance value = 20 x 10⁵

= 2,000,000Ω

= 2 MΩ

Maximum value = 2,000,000 x 1.10

= 2,200,000Ω

Minimum value = 2,000,000 x 0.90

= 1,800,000Ω

(iii) Orange Brown Blue and Gold

Orange = 3, Brown = 1, Blue = Multiplier (10⁶), Gold = ±5%

Resistance value = 31 x 10⁶

= 31,000,000Ω

= 31 MΩ

Maximum value = 31,000,000 x 1.05

= 32,550,000Ω

Minimum value = 31,000,000 x 0.95

= 29,450,000Ω

(iv) Blue Black Black and Silver

Blue = 6, Black = 0, Black = Multiplier (10⁰), Silver = ±10%

Resistance value = 60 x 10⁰

= 60Ω

Maximum value = 60 x 1.10

= 66Ω

Minimum value = 60 x 0.90

= 54Ω

(v) Brown Blue Red and Gold

Brown = 1, Blue = 6, Red = Multiplier (10²), Gold = ±5%

Resistance value = 16 x 10²

= 1600Ω

Maximum value = 1600 x 1.05

= 1680Ω

Minimum value = 1600 x 0.95

= 1520Ω

===========================

(2a)

(i) Electromotive force (EMF): Electromotive force, denoted as EMF represents the electrical energy per unit charge that a source of electrical energy can provide. It is measured in volts (V).

(ii) Potential difference: Potential difference is the difference in electric potential between two points in an electric circuit, representing the work done per unit charge in moving a charge between those two points. It is measured in volts (V).

(iii) Current: Current is the flow of electric charge through a conducting medium, measured as the rate of flow of charge through a given cross-sectional area. It is measured in amperes (A).

(2b)

Given:

Voltage (V) = 240V

Current (I) = 2.4A

Total Resistance (RT) = V/I

RT = 240/2.4

RT = 100Ω

Total Resistance (RT):

= Sum of parallel resistance (RP) + Sum of series resistance (RS)

RP = RT – RS

RS = 70Ω

RP = 100 – 70

RP = 30Ω

1/RP = 1/90 + 1/B

1/30 = 1/90 + 1/B

1/B = 1/30 – 1/90

1/B = (3 -1)/90

1/B = 2/90

B = 90/2

B = 45Ω

===========================

(3a)

(i) Voltage reaches its maximum level

(ii) Charging current drops to minimum

(iii) Battery temperature stabilizes

(3b)

Given:

Number of identical cells = 9

Electromotive force (EMF) = 2v

Internal resistance = 0.1Ω

Resistance Load = 7.5Ω

(i) All In Series:

Total EMF = 9 x 2

= 18v

Total internal resistance = 9 x 0.1

= 0.9Ω

Total resistance = 0.9 + 7.5

= 8.4Ω

Current = 18/8.4

= 2.14A

Potential difference across the load:

= 2.14 x 7.5

= 16.05Ω

(ii) All Cells in Parallel:

Total EMF = 2v

Total internal resistance = 0.1/9

= 0.0111Ω

Total resistance = 0.0111 + 7.5

= 7.5111Ω

Current = 2/7.5111

= 0.266A

Potential difference across the load:

= 0.266 x 7.5

= 1.995Ω

(iii) 3 Cells in Series and 3 Sets in Parallel:

Total EMF in series:

= 3 x 2

= 6v

Total internal resistance in series:

= 3 x 0.1

= 0.3Ω

Total EMF in parallel = 6v

Total internal resistance in parallel:

= 0.3/3

= 0.1Ω

Total resistance = 0.1 + 7.5

= 7.6Ω

Current = 6/7.6

= 0.789A

Potential difference across the load:

= 0.789 x 7.5

= 5.92Ω

===========================

(5a)

(i) Inductive reactance is the opposition that an inductor offers to the flow of alternating current. Its unit of measurement is the ohm (Ω).

(ii) Capacitive reactance is the opposition that a capacitor offers to the flow of alternating current. Its unit of measurement is the ohm (Ω).

(iii) Impedance is the total opposition that a circuit offers to the flow of alternating current. It is a combination of resistance, inductive reactance, and capacitive reactance, measured in ohms (Ω).

(5b)

Given:

Voltage (V) = 100 V

Frequency (f) = 50 Hz

Resistor (R) = 10 Ω

Inductance (L) = 50 mH

= 0.05 H

Capacitance (C) = 350 μF

= 350 × 10⁻⁶F

(i) Current (I):

Inductive reactance (XL) = 2πFL

XL = 2 x π x 50 x 0.05

XL = 31.42Ω

Capacitive reactance (XC)= 1/(2πFC)

XC = 1/(2 x π x 50 x 350 x 10⁻⁶)

XC = 91.09Ω

Total impedance (Z):

1/Z = 1/R + 1/XL + 1/XC

1/Z = 1/10 + 1/31.42 + 1/91.09

1/Z = 0.1+ 0.0318 + 0.01098

1/Z = 0.14278

Z = 1/0.14278

Z = 7.0Ω

Current (I) = V/Z

I = 100/7.0

I = 14.29A

(ii) Power Factor:

PF = R/Z

PF = 10/7.0

PF = 1.43

(iii) Angle of Lag (θ):

θ = Cos⁻¹(PF)

θ = Cos⁻¹(1)

θ = 0°

(iv) Power Consumed by the Circuit:

P = VI Cosθ

P = 100 x 14.29 Cos(0)

P = 100 x 14.29 x 1

P = 1429W

===========================

(6a)

(i) Accuracy

(ii) Resolution

(iii) Response time

(6b)

(i) 0 – 5 mA:

R = (50×10⁻³x50)/ (5×10⁻³)

R = 500Ω

(ii) 0 – 10 A:

R = (50×10⁻³x50)/ 10

R = 0.25Ω

(iii) 0 – 15 A:

R = (50×10⁻³x50)/ 15

R = 0.167Ω

(iv) 0 – 50 V:

R = 50/(50×10⁻³)

R = 1kΩ

(v) 0 – 100 V:

R = 100/ (50×10⁻³)

= 2kΩ

(vi) 0 – 150 V:

R = 150/ (50×10⁻³)

R = 3kΩ

===========================

(7a)

(i) Heating Effect: When an electric current flows through a conductor, it produces heat due to the resistance of the material. This is commonly used in devices such as electric stoves and toasters to generate heat.

(ii) Magnetic Effect: An electric current flowing through a conductor creates a magnetic field around it. This principle is the basis for electromagnets used in various applications such as electric motors and transformers.

(iii) Chemical Effect: Electric currents can cause chemical reactions in certain materials. This effect is utilized in processes like electroplating and electrolysis, where a chemical change is induced by passing an electric current through a solution.

(7b)

Given:

Resistance (R) = 30Ω

Voltage (V) = 240V

Time (t) = 1 hour = 3600 seconds

Power (P) = V²/R

P = (240)²/30

P = 1920W

Energy consumed (E):

E = Power x Time

E = 1920 x 3600

E = 6,912,000J

E = 6,912,000/3,600,000

E = 1.92kWh

===========================

COMPLETED

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