Please Log in or Register for more.

What is the back EMF?

107 views

1 Answer

Answer :

When the armature of a d.c. motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator. The induced e.m.f.acts in opposite direction to the applied voltage V (Lenz's law) and in known as backor counter e.m.f.(Eb)

The back emf Eb(= PΦZN/60 A) is always less than the applied voltage V, although this difference is small when the motor is running under normal conditions.

Back emf in dc motor

A shunt wound dc motor shown in figure below. When dc voltage V is applied across the motor terminals, the field magnets are excited and armature conductors are supplied with current. Therefore, driving torque acts on the armature which begins to rotate. As the armature rotates, back emf Eb is induced which opposes the applied voltage V.

image

The applied voltage V has to force current through the armature against the back emfEb. The electric work done in overcoming and causing the current to flow against Eb is converted into mechanical energy developed in the armature. It follows, therefore, that energy conversion in a d.c. motor is only possible due to the production of back emf.

Like 0 like

Please log in or register to answer this question.

Related Questions


What is back emf? 
Last Answer : Back EMF: When a current carrying conductor is placed in a magnetic field it experiences a force; when it moves due to the force it (conductor) cuts the magnetic field due to which an emf is ... (hence the applied armature voltage) is opposed by the induced emf which is therefore called as Back emf.

Show More

91 views 1 answer







Do AC induction motors have back EMF?

Show More

71 views 0 answers







What is back EMF of synchronous motor?

Show More

77 views 0 answers







What is back EMF in inductor?

Show More

138 views 0 answers







What is the back EMF in Transformers?

Show More

77 views 0 answers







What is the back EMF of a dc motor?

Show More

2.6k views 0 answers







What is the back EMF of the motor?

Show More

68 views 0 answers







The back emf of synchronous motor depends on?
Last Answer : The back emf of synchronous motor depends on load angle.

Show More

65 views 1 answer








Last Answer : The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is 0.5.

Show More

324 views 1 answer








Last Answer : In case of D.C. shunt motors the speed is dependent on back e.m.f. only because flux is practically constant in D:C. shunt motors.

Show More

250 views 1 answer








Last Answer : The armature may burn if the back e.m.f. of a D.C. motor vanishes suddenly.

Show More

423 views 1 answer







Self induced emf and Mutually induced emf
Last Answer : (i) Self-induced e.m.f.: The e.m.f. induced in a coil due to the change of its own flux linked with it, is called self-induced e.m.f.  (ii) Mutually induced e.m.f.: The e.m.f. induced in a coil due to the changing current in the neighbouring coil, is called mutually induced e.m.f. 

Show More

140 views 1 answer







What is Phase sequence? Draw waveforms of 3 phase emf.
Last Answer : Phase sequence: It is the order in which the three phases reach their peak or maximum values. It is shown in below fig. the phase sequence is A-B-C (or R-Y-B). In the following waveforms, it is ... 120º, B- phase voltage attains its positive maximum value. So the phase sequence is R-Y-B. 

Show More

125 views 1 answer







Compare statically induced emf with dynamically induced emf on any four points.
Last Answer : Statically induced emf Dynamically induced emf Emf is induced without any relative motion between conductor and magnetic field. Emf is induced due to relative motion between conductor ... induced in transformer windings e.g emf induced in Generator, Alternator armature windings

Show More

1.1k views 2 answers







Explain the term self induced EMF with a neat diagram.

Show More

84 views 0 answers







Define: 1) statically induced EMF 2) dynamically induced EMF Write the names of equipments in which these two types of EMF get induced
Last Answer : Concept of statically induced emf: The emf induced in coil or conductors without any relative motion between it and magnetic field is called statically induced emf. When conductor is stationary and flux ... it. This emf is dynamically induced emf. e.g. Emf induced in generators, alternator.

Show More

882 views 3 answers







List the two types of induced EMF.
Last Answer : There are two types of EMF one is statically induced EMF and second is dynamically induced EMF.

Show More

117 views 1 answer







Explain dynamic and static induced emf with neat diagram.
Last Answer : Dynamically Induced EMF:-  In this case, either coil moves or magnet moves, so that there is relative motion between coil & magnetic field. Thus magnetic field is cut by coil & emf is induced in it. The emf ... The expression for induced EMF is e= -L(di/dt) or = -N(dϕ/dt).

Show More

593 views 1 answer







129 views 0 answers







The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is  (1) 1000V (2) 100V (3) 600V (4) 10,000V
Last Answer : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is 1000V

Show More

370 views 1 answer







The fractional-pitch used for eliminating 7th harmonic from the emf wave of an alternator is (A) 2/3 (B) 5/6 (C) 7/8 (D) 6/7
Last Answer : The fractional-pitch used for eliminating 7th harmonic from the emf wave of an alternator is 6/7

Show More

494 views 1 answer







What is the EMF equation of the transformer?
Last Answer : E1 =2(3.142)fN1 (flux)1E2 =2(3.142)fN2(flux)2

Show More

170 views 1 answer







How can I apply a cream to my back where I can't reach?
Last Answer : I have found that I can reach more of my back with the back of my hand. Can you put some cream on the back of your fingers and try? Another idea is to buy a back scratcher that has a flat side and use it to apply the cream.

Show More

2 views 1 answer







Do you have any ideas to bring back my parents back together?
Last Answer : All you can do is talk to them about your feelings. I would do it with each one individually. Then the rest is up to them if they want it. Even as a family member you don't know what the ... split them apart. It's a little hard to imagine that they would get back together after seven years. Hugs.

Show More

0 views 1 answer







Why does getting your back scratched feel so good?
Last Answer : I think it has something to do with our veins LOL

Show More

1 view 1 answer







How do you prevent chronic back pain from turning you into a bitter recluse?
Last Answer : I do yoga and then find a sunny window to meditate by!

Show More

1 view 1 answer







Is there such a thing as a truly comfortable futon that won't give you back problems?
Last Answer : My personal experience with futons has not been good. They have thin mattresses on hard wooden slats. What’s to love? Consider another type of bed or a couch/bed.

Show More

1 view 1 answer







I have a pain in my back right under my shoulder blade and when I move fast it hurts bad but if i move very slow its ok, what could that be?
Last Answer : It could be a lot of different things, ranging from easily dismissible to very serious. You don’t want to mess around or take half measures when it comes to your back – this may call for a doctor’s visit. A physical therapist could probably help you, too.

Show More

2 views 1 answer







IS it normal for my back to hurt more after beginning to see a chiropractor?
Last Answer : The only way to know for sure is to have a MD examine you and/or image your back. I love Chiropractors and I am very good friends with 3 in town, acquaintances with many more. Each practice ... assume for you. If it's fine then go back to the chiropractor. Luckily you have good health insurance.

Show More

1 view 1 answer







Back Pain help?
Last Answer : my back pain was cured by a dr named john sarno. Google him and something called TMS. Tension myositis syndrome. Have an open mind. I’m living proof he cures.

Show More

1 view 1 answer







How can men find it comfortable to sit on their wallet when it is in their back pocket?
Last Answer : Status symbol. We think you’re actually checking us out back there.

Show More

2 views 1 answer







How to Strengthen Your Lower Back
Last Answer : How to Strengthen Your Lower Back Your lower back is usually the most common body part taken for granted when working out. Most people concentrate more on their extremities and abdomen that they forget to ... lower ab exercises and as an addition, learn the Top 10 ways to stay motivated to exercise.

Show More

3 views 1 answer







How to Float On Your Back
Last Answer : How to Float On Your Back Floating on your back is usually one of the first tricks a new swimmer will learn. It's easy to see why: It doesn't involve paddling, kicking or anything extreme ... in place, you can start moving around by doing little flutter kicks to the direction you want to go.

Show More

1 view 1 answer







How to Back Dive
Last Answer : How to Back Dive Eager to impress your friends while having fun in the pool? Regular, forward dives are very common, so if you want to try something unique, you can do a back dive ... this new diving technique. Your friends will surely explode into applause as you perform a perfect back dive.

Show More

3 views 1 answer







How To Give a Back Massage
Last Answer : How To Give a Back Massage Nothing beats a soothing back massage after a stressful day in the office or exercising. This type of massage is ideal for those who would like to increase ... you can certainly provide comfort and relief with the right practice and application of the correct techniques.

Show More

6 views 1 answer







Symptoms of Back Pain Causes And Tips
Last Answer : Symptoms of Back Pain Causes And Tips Back pain is the most common complaint heard among the adults these days. It has been estimated that people do suffer from back pain at least once in their ... night sleep that will recover from all the bodily disorders and you wake up fresh the next morning.

Show More

11 views 1 answer







The counter e.m.f. of a d.c. motor?
Last Answer : The counter e.m.f. of a d.c. motor helps in energy conversion.

Show More

90 views 1 answer








Last Answer : E.m.f. of a Weston cell is accurately measured by electrostatic voltmeter.

Show More

205 views 1 answer








Last Answer : It is required to measure the true open circuit e.m.f. of a battery. The best device is D.C. potentiometer.

Show More

284 views 1 answer








Last Answer : If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by Blv.

Show More

242 views 1 answer








Last Answer : When the armature of a D.C. motor rotates, e.m.f. induced is back e.m.f.

Show More

203 views 1 answer







Why do I keep thinking about divorced parents?
Last Answer : Perhaps some of the ideas in this article will help you.

Show More

1 view 1 answer







Could the Ibuprofen be making this difference?
Last Answer : answer:Could very well be. I live on ibuprofen.

Show More

1 view 1 answer







How to deal with the problem of lumbar bone fusion?
Last Answer : Why would you want her not to get proper treatment? There is nothing aside from surgery that would fix bones fusing together.

Show More

1 view 1 answer







What does Worker's Comp have to do with whether or not a doctor will treat you?
Last Answer : There are doctors specifically trained in Workers Comp procedures from what I understand. My husband got hurt on a job and could only go to one specific knee surgeon and he hated him (sub par idiot) so he had to request another. That’s what I got out of it, may not be right.

Show More

2 views 1 answer







I can't loosen up this stiff neck. Any suggestions?
Last Answer : answer:Are you holding your breath and tense when getting a massage from the boyfriend? Try deep breathing and RELAX your body. Do this after a long hot bath, and also, try rolling your upper ... with hot water jets. You must be relaxed though. Achieving DEEP relaxation is key to muscle tension.

Show More

1 view 1 answer







Herniated disc sufferers: what has worked for you?
Last Answer : Yoga. I am not telling you to ignore your doctors but they all failed me miserably and I needlessly suffered while they ordered more tests. 2 months later I was not better off until I found Yoga. In 3 ... of doctors and Chiro's could .I healed with Yoga. And 11 years later no pain what so ever.

Show More

1 view 1 answer







Suddenly my shoulders hurt terrible, and burn! Any doctors in the house?
Last Answer : answer:I have no idea. Have you strained yourself lately? Maybe some sort of heartburn, or muscle spasms. I’d check with your doctor if the pain does not subside, or becomes worse in the next few hours. Maybe you are sprouting wings. lol

Show More

1 view 1 answer







Is there a cure for Tietze Syndrome?
Last Answer : answer:It’s talking about shoving you around with a chiropractic “treatment.” Tietze’s syndrome, or costochondritis is a cartilage inflammation of your shoulder. Chiropractic won’t help, as it doesn’t help just about anything. Real treatments are found on the linked website.

Show More

1 view 1 answer







What is good posture, and how does one maintain it?
Last Answer : answer:Good posture gives you height, gives the appearance of confidence, and I am thinking is better overall for back health. I have been losing my good posture from sitting and laying around too ... help with posture, most dance for that matter, along with demanding it of yourself in general.

Show More

0 views 1 answer






Show More⇦ PreviousNext ⇨