Electrical Engineering Answers

Two resistors when connected in series have a total resistance of 40 ohms and when connected in parallel

has a total resistance of 7.5 ohms. Find the value of each resistor in ohm 

What is the equivalent area in sq. inch for a conductor 336 400 circular mil?

1.1 Medupi power station uses coal of calorific value of 5880 kcal/kg to generate electricity. They use 14.3 tonnes of coal every 25 minutes to generate the maximum demand of the power station. The thermal and electrical efficiency of the power station are 24.2% and 81.1%, respectively. The cost of purchasing the coal is R800 per tonne.

1. Determine the overall efficiency of the power station (%). 

A 20 kVA closet transformer located inside a building is used to step down the voltage for the building. It is connected to a primary 4800 V AC power source. The ratio of the number of primary windings to the number of secondary windings on the transformer is 20 to 1 and 40 to 1.

a. Approximate the secondary voltage provided.

b. Approximate the current available, in amps

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(5) Compared to a PN junction with NA = ND = 1014 cm-3, which one of the following 

statements is TRUE for a PN junction with NA = ND = 1020 cm-3? ( ).

A. Reverse breakdown voltage is lower and depletion capacitance is lower 

B. Reverse breakdown voltage is higher and depletion capacitance is lower 

C. Reverse breakdown voltage is lower and depletion capacitance is higher 

D. Reverse breakdown voltage is higher and depletion capacitance is higher 

(6) Gold is often diffused into silicon PN junction devices to ( ). 

A. increase recombination rate B. reduce recombination rate 

C. make silicon a direct gap semiconductor D. make silicon semimetal