1 Answer

Answer :

Copper brushes in D.C. machine are used where low voltage and high currents are involved.

Related questions

Last Answer : The rapid wear of brushes takes place due to abrasion from dust, excessive spring pressure, rough commutator bars, high mica insulation between com-mutation bars.

Last Answer : Armature coil is short circuited by brushes when it lies along neutral axis.

Last Answer : The number of brushes in a commutator depends on amount of current to be collected.

Last Answer : The material for commutator brushes is generally carbon.

Last Answer : Brushes of D.C. machines are made of carbon.

Last Answer : In lap winding, the number of brushes is always same as the number of poles.

Description : Brushes of DC machine are made up of ?

Last Answer : Brushes of DC machine are made up of carbon.

Description : In a DC motor, it is important to place the brushes along ______ A) Magnetic Neutral Axis B) Normal Geometric Axis C) Nominal Geometric Axis D) None of these

Last Answer : In a DC motor, it is important to place the brushes along Magnetic Neutral Axis

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Description : How to Patina Copper

Last Answer : How to Patina Copper Patina is that tarnish coating that develops outside metal, like copper, over time. Not only does it add an attractive appearance to copper, but it also provides protection to harsh ... egg. Once you've reached the desired patina coat, rinse the copper pieces in lukewarm water.

Description : How to Clean Copper

Last Answer : How to Clean Copper Whether it's a coin, a pan, or a trophy, copper has one of the nicest-looking finishes among common metals. Copper can retain its finish for quite a while, although it is ... properly. With these tips, you'll never have to worry about your copper items losing their shine again.

Description : Select insulating materials for following parts : (i) Insulation between heating element and base plate of electric iron. (ii) Insulation used over copper or aluminium conductor used for making coils. (iii) Transformer bushings. (iv) Insulation between transmission line and pole.

Last Answer : Parts Insulating Materials  Insulation between heating element and base plate of electric iron. Mica Insulation used over copper or aluminium conductor used for making coils.  ... Transformer bushings Porcelain  Insulation between transmission line and pole. Porcelain

Description : Why is aluminium used instead of copper for overhead cables?

Last Answer : Because copper reacts with atmosphere variation and it's cost High as compared to aluminium and aluminium is good property and less cost so aluminium is used

Description : Which is a semiconductor: copper, silicon, or neon?

Last Answer : Copper is a metal. Silicon is a semiconductor. Neon is inert gas.

Description : Compare copper and aluminium.

Last Answer : Copper Aluminium Resistivity is less Resistivity is more More weight Low weight Mechanically strong Mechanically weaker Specific Gravity high Specific Gravity Low ... Tensile strength is half of that of copper Used for winding Used for overhead lines

Description : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is

Last Answer : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is 0.707

Description : At full -load of a transformer, the iron loss and copper loss are 3000 W and 4000 W respectively. Then total loss at maximum efficiency is :  (A) 7000 W (B) 6000 W (C) 8000 W (D) 4000 W

Last Answer : At full -load of a transformer, the iron loss and copper loss are 3000 W and 4000 W respectively. Then total loss at maximum efficiency is : 6000 W

Description : Two copper conductors have equal length. The cross-sectional area of one conductor is four times that of the other. If the conductor having smaller cross-sectional area has a resistance of 40 ohms the resistance of other conductor will be?

Last Answer : Two copper conductors have equal length. The cross-sectional area of one conductor is four times that of the other. If the conductor having smaller cross-sectional area has a resistance of 40 ohms the resistance of other conductor will be 10 ohms.

Last Answer : The ground wire should not be smaller than No 10 copper.

Description : Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is?

Last Answer : Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is approximately equal to 1.

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Description : explain skin effect in copper interconnects. what are the various ways of reducing this effect?

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Description : In a DC shunt generator working on load, the brushes are moved forward in the direction of rotation, as a result of this, commutation will   (a) Improve but terminal voltage will fall   (b) ... will fall   (c) Improve and terminal voltage will rise   (d) worsen and terminal voltage will rise 

Last Answer : In a DC shunt generator working on load, the brushes are moved forward in the direction of rotation, as a result of this, commutation will Improve but terminal voltage will fall 

Last Answer : If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be crossmagnetisation as well as demagnetising.

Last Answer : In D.C. generators, the brushes on commutator remain in contact with conductors which lie under interpolar region.

Description : Copper brushes in D.C. machine are used (a) where low voltage and high currents are involved (b) where high voltage and small cur-rents are involved (c) in both of the above cases (d) in none of the above cases

Last Answer : Ans: a

Description : Etched or burned bands on the contact faces of the brushes in a direct current generator can be caused by ____________. A. high mica segments B. copper drag on the commutator C. brushes improperly positioned D. copper embedded in the brushes

Last Answer : Answer: C

Description : The material for commutator brushes is generally (a) mica (b) copper (c) cast iron (d) carbon

Last Answer : Ans: d

Description : Brushes of D.C. machines are made of (a) carbon (b) soft copper (c) hard copper (d) all of above

Last Answer : Ans: a

Description : Seating the brushes on a D.C. motor is first accomplished using ________________. A. a file for cutting the approximate curvature followed by sandpaper for the final fit B. sandpaper with the motor not ... for the finishing cut D. course lapping compound, followed by a medium and then a fine grade

Last Answer : Answer: B

Description : Voltage generated by most AC generators is fed from the machine to the bus by means of ____________. A. brushes on a commutator B. brushes on slip rings C. slip rings on a commutator D. direct connections from the stator

Last Answer : Answer: D

Description : In a d.c. machine, the armature mmf is (A) stationary w.r.t. armature. (B) rotating w.r.t. field. (C) stationary w.r.t. field. (D) rotating w.r.t. brushes.

Last Answer : (C) stationary w.r.t. field.

Last Answer : In a D.C. machine stray loss is the sum of iron loss and mechanical loss.

Last Answer : In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called armature.

Last Answer : To avoid formation of grooves in the commutator of a D.C. machine the brushes of opposite polarity should track each other.

Last Answer : Open circuited armature coil of a D.C. machine is identified by the scarring of the commutator segment to which open circuited coil is connected and indicated by a spark completely around the commutator.

Last Answer : In case of D.C. machine winding, number of commutator segments is equal to number of armature coils.

Description : Eddy currents are induced in the pole shoes of a D.C. machine due to?

Last Answer : Eddy currents are induced in the pole shoes of a D.C. machine due to relative rotation between field and armature.

Last Answer : Armature reaction of an unsaturated D.C. machine is crossmagnetising.

Last Answer : Iron losses in a D.C. machine are independent of variations in load.

Last Answer : In a four-pole D.C. machine alternate poles are north and south.

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Last Answer : I think it’s brilliant. It takes just as much talent to create a piece of work like that as it does with a real brush and paint.

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Last Answer : Electric motor has 1 carbon brush.