Electric Circuits Answers

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A restaurant uses five 80% energy efficient 30 W bulbs, a refrigerator marked “240 V, 5A” and a 1.5
kW electric cooker. These loads are connected to 220 V mains supply. The bulbs, refrigerator and
electric cooker are switch on for 12 hours, 24 hours and 5 hours respectively on daily average. The
restaurant opens six days a week – all loads are switched off throughout the 7th day.
(a) Determine the resistance of the refrigerator.
(b) (i) Calculate the electrical power in the refrigerator when plugged to the 220 V power outlet.
(ii) Calculate the input power of each light bulb.
(iii) At what rate is energy consumed by the restaurant?
(c) If the restaurant needs a single fuse to protect all its devices, recommend the rating of the fuse in
amperes.
(d) Calculate the daily energy consumption of the restaurant.
(e) If PHCN charges ₦32 per kWh, calculate the monthly (4 weeks) bill.

Two batteries P and Q each of Emf 8 V and 3 V have internal resistance of 2 Ω and 4 Ω respectively.
Calculate the values of the current through the circuit.

A wire 1.0m long and with cross sectional area 2.0×10^-7m^2 has a resistance of 0.1Ω calculate the electrical conductivity of the wire

Calculate the length of a constant wire of cross sectional areas 4π x 10^8m and resistivity 1.1 x 10^-6Ωm required to construct a standard resistor of resistance 21Ω (take π=22/7)

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the mathematical comparisons of energy/power loss of transmitting electricity at
different voltages. Produce a qualitative, reasoned argument which identifies why.

Suppose a DC power source with a voltage of 45 volts is connected to a 15 Ω load. How much power will this load dissipate?

A 1.5 volt battery is connected to a 10 ohm resistor. What current passes through the resistor?

the voltages used to transmit electricity through the national grid for a variety of uses, have been selected and why they may be different at different points in the transfer system