HW11

The resistance of the copper field winding of a dc machine at 40 degree Celsius is 0.40 ohms. After operating for some time, the resistance is found to be 0.50 ohms. Find the operating temperature.

Explain Ampere’s law.

The two basic kinds of electricity are: Static and stationary. Current and resistance. a. b. Static and dynamic. d. Dynamic and moving. C. Electromotive force (EMF) causes electrons to flow through a circuit. EMF is measured in: Volts. b. Amperes. Current, Resistance a. C. d. A complete circuit is made up of A generator, electron flow. and voltage source. a. A source of electricity, a conductor, and a consuming device. b. A consuming device, a load, and a conductor. d. Electron flow, resistance, and a load. C. You can get an electrical shock: When some part of your body becomes part of an electric a. circuit. b. If you touch both wires of an electric circuit. C. If you touch one wire of an energized circuit and ground. d. All of the above. Electricity can cause fires: Because of defective or misused electrical equipment. When wires are improperly spliced or connected. When wires are improperly connected to outlets or a. b. C. switches. d. All of the above.

Explain the breakdown in liquid? Discuss the different methods of measuring high dc voltages. What are the limitations in each method?

How open circuit test can be performed? Which type of losses can be found using this test? Subject Electrical machine

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Discuss in detail the motor that are commonly employed for electric vehicular application

What is Ohm's Law of magnetic circuit? Derive relation between electric and magnetic circuit.

In a 6-pole DC machine, 90 mechanical degrees corresponds to how many electrical degrees? (a) 270 (b) 180 (c) 30 (d) 45

Explain the Working Principle used in Eddy Current .

A dc-source has positive and negative polarities. Is it correct to say that an ac-voltage source has no polarity? Why or why not?

Discuss how electricity is generated from a wind turbine.

If you placed a bar of ion inside a cylindrical coil of wire, and then run dc through the wire, you have: a. a rheostat b. a permanent magnet c. a flux meter d. an electromagnet

a) What is skin effect? b) Explain why it is occurring in AC not in DC.

What is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current?a. AC electrical generatorb. armaturec. alternatord. magnetic field

What are the different losses which occur in a DC machine. * Your answer

Subject : electrical machines

A 10 pole d.c. machine has a lap wound armature. It has 600 conductors, each of resistance 0.05 ohm. What is the armature resistance

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What are the basic components of Steam Power Plant.

A 220 V DC Machine supplies 20 A at 200 V as a generator. The armature resistance is 0.2 ohm. If the machine is now operated as a motor at the same terminal voltage and current but with the flux increased by 10 percent, the ratio of motor speed to generator speed will be

The interpoles in DC machines are: O a. Used to maintain constant magnetic flux O b. Used to increase the cost of the machine O c. Used to maintain the speed of rotation O d. Used to reduce the sparks

A)The left hand rule for a coil is such that if you were to hold a coil in your left hand with your fingers pointing in the direction of the electron flow, your thumb would point in the direction of thea) electron flow b) flow lines c) face of the north pole d) none of the above. B) What is a magnetic flux line?a) It is the space around a magnet or the space in which the magnetic forces act.b) It is the magnetic force that has a definite direction at all points along a curved line from the north to south pole.c) It is the ability of a magnetic material to be easily magnetized.d) none of the above C)It is believed that a magnetic material is .........a) consists of a single large magnetic molecule b) is composed of many tiny magnetic molecules c) consists of a single non-magnetic molecule d) none of the above

How can the polarity of an electromagnet be determined if the direction of current flow is known?   2. Define the following terms:   3. flux density     4. Permeability     5. Reluctance     6. Saturation   Unit 13 Magnetic Induction       7. Name three factors that determine the amount of induced voltage in a coil.   8. What is the effect on induced voltage of adding more turns of wire to a coil?   9. Into how many time constants is an exponential curve divided?     10. Each time constant of an exponential curve is equal to what percentage of the maximum amount of charge?       11. An inductor has an inductance of 0.025 H and a wire resistance of 3 . How long will it take the current to reach its full Ohm's law value?                             Unit 15 Alternating Current   . 12 What is the most common type of AC waveform?   13 How many degrees are there in one complete sine wave?   14 At what angle does the voltage reach its maximum negative value on a sine wave?   15 A sine wave…

The armature of a d.c. The machine has a resistance of 0.25 ohm and is connected to a 300V supply. Determine the e.m.f. generated when it runs as a generator giving 100 A and as a motor taking 80 A. please check the back emf calculations