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Browse complete papersA half-wave rectified sine wave has a peak value of 20 V. What is its average value?
20 V
Correct answer
An electric traction motor drives a train with a total mass of \(50,000 \text{ kg}\). The train accelerates from rest to a speed of \(60 \text{ km/h}\) in \(30 \text{ seconds}\). If the tractive effort is constant and there are no losses, what is the value of the tractive effort?
\(27.8 \text{ kN}\)
\(55.6 \text{ kN}\)
\(46.8 \text{ kN}\)
\(35.2 \text{ kN}\)
Correct answer
\(27.8 \text{ kN}\)
A resistance welding machine is used to weld two steel plates. A current of 5000 A flows through the weld. If the resistance of the weld joint is 150 \(\mu\Omega\), what is the heat generated at the weld in 0. 5 seconds?
Correct answer
A three-phase electric furnace with a star-connected resistive load of \(20~\Omega\) per phase is connected to a \(400~V\) line-to-line a.c. supply. What is the total heat generated by the furnace in \(30\) minutes?
Correct answer
A steel component with a surface area of \(0.2 m^2\) is to be electroplated with a \(20 \mu m\) thick layer of copper. A current of \(50 A\) is passed through a copper sulfate solution. The density of copper is \(8960 kg/m^3\), and the electrochemical equivalent of copper is \(0.329 mg/C\). How long will the electroplating process take?
Correct answer
A three-phase transformer is connected in a star-delta \((Y-\Delta)\) configuration. The line voltage on the star side is 11 kV, and the transformer has a turns ratio per phase of 20:1. What is the line voltage on the delta side?
Correct answer
A three-phase transformer has a rating of \(150 kVA\). The line voltages are \(11 kV\) on the primary and \(400 V\) on the secondary. If the transformer is star-connected on both sides, what is the phase current on the primary side?
Correct answer
A 100 kVA, 11000/400 v transformer has an iron loss of 800 W. The full-load copper loss is 1200 W. At what load (in kVA) will the efficiency be maximum?
Correct answer
A 5 kw, 200 v d.c. motor has total losses of 1 kW. What is the efficiency of the motor?
50%
Correct answer
A 250 V d.c. series generator with a total internal resistance of 0. 2 \(\Omega\) delivers a load current of 50 A. What is the generated EMF?
255 V
260 V
250 V
265 V
Correct answer
255 V