Electrical Installation - Scientific Principles

Front

What application is mineral insulated cable particularly suitable for?

Back

Fire alarm cable

Answer explanation

Mineral insulated cable is particularly suitable for fire alarm systems due to its high resistance to heat and fire, ensuring reliable operation in emergencies, unlike other applications like domestic sockets or lighting.

Front

What application is thermosetting steel wire armoured cable particularly suited to?

Back

Feeding an outbuilding

Answer explanation

Thermosetting steel wire armoured cable is particularly suited for feeding an outbuilding due to its durability and ability to withstand harsh conditions, making it ideal for outdoor installations.

Front

What is the resistance of 120m of copper 4mm2 cable if it has a resistivity of 0.0178μΩ/m?

Back

0.534Ω

Answer explanation

To find the resistance, use the formula R = ρL/A. Here, ρ = 0.0178μΩ/m, L = 120m, and A = 4mm² = 4 x 10^-6 m². Calculating gives R = (0.0178 x 120) / (4 x 10^-6) = 0.534Ω, which is the correct answer.

Front

Steel conduit with a resistivity of 0.18μΩ/m and an overall CSA of 25mm2 is to be used as a circuit CPC. What is the resistance if the conduit run is 25m?

Back

0.18Ω

Answer explanation

To find the resistance, use the formula R = ρL/A. Here, ρ = 0.18μΩ/m, L = 25m, and A = 25mm². Converting 25mm² to m² gives 0.000025m². Thus, R = (0.18 x 10^-6) x 25 / 0.000025 = 0.18Ω.

Front

If resistors are added up to find the total circuit resistance, what type of circuit is it?

Back

Series

Answer explanation

In a series circuit, resistors are added directly to find the total resistance. This means the total resistance is the sum of individual resistances, confirming that the correct answer is 'Series'.

Front

If resistors are added up using reciprocals to find the total circuit resistance, what type of circuit is it?

Back

Parallel

Answer explanation

In a parallel circuit, the total resistance is calculated using the reciprocal formula: 1/R_total = 1/R1 + 1/R2 + ... This differs from series circuits, where resistances are simply added. Thus, the correct answer is 'Parallel'.

Front

What is the resistance of a circuit if the current drawn from a 400V supply is 25A?

Back

16Ω

Answer explanation

Using Ohm's Law (V = I × R), we can rearrange to find resistance (R = V/I). Substituting the values, R = 400V / 25A = 16Ω. Therefore, the correct answer is 16Ω.

Front

What current is drawn from a 230V supply if a 6Ω load is connected?

Back

38.3A

Answer explanation

Using Ohm's Law (I = V/R), the current I is calculated as I = 230V / 6Ω = 38.33A. Therefore, the correct answer is 38.3A.

Front

Which of the following is not an ohms law equation? V=RI, V=IR, I=V/R, R=VI

Back

R=VI

Answer explanation

The equation R=VI is incorrect according to Ohm's Law. Ohm's Law states V=IR, I=V/R, and R=V/I. Therefore, R=VI does not represent a valid relationship in Ohm's Law.

Front

If four equal resistors are connected in series across a 200V supply, what will be the voltage across a single resistor?

Back

50V

Answer explanation

In a series circuit, the total voltage is divided equally among the resistors. With four equal resistors across a 200V supply, the voltage across each resistor is 200V / 4 = 50V. Thus, the correct answer is 50V.