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What is EMF??

What actually is EMF?? for example if a question says: four identical cells, each of e.m.f 1.5V and internal resistance 0.1 ohms are connected in series. What current will this combination of cells drive through a bulb of resistance 2.0 ohms?? so you have I=VR.. so would V = 1.5 x 4?? so The EMF is basically another term to say each battery is 1.5V or is it something completely different??
Also could you explain in simple terms because i'm a single science gcse student going to A level physics so am just getting to terms with all the other terms for each unit etc...
Thanx :biggrin:

Reply 1

Steeeeevo

15

well EMF stands for Electromagnetic field (if you didnt know) but im not a physist so I cannt help you any more than that. sorry.

Reply 2

Eddie K

2

EMF is a measure of the strength of a source of electrical energy. For example, a battery which has a sticker on the side indicating it is a 9V battery has an EMF of 9V. In practice, this value is very slightly less because of the internal resistance of the battery, which you will learn about very soon.

Unfortunately, EMF in this context does not stand for "Electromagnetic Field", but instead "Electromotive Force". The reason for this is historical and is irrelevant to any of your studies - just be sure to remember what EMF is, that will be enough.

Reply 3

rainy_skye

OP

oki doki, just been doing a bit about internal resistance so am slightly confused by it all. so how would i work out this queston?? four identical cells, each of e.m.f 1.5V and internal resistance 0.1 ohms are connected in series. What current will this combination of cells drive through a bulb of resistance 2.0 ohms??

Reply 4

REME-Bod

1

rainy_skye

oki doki, just been doing a bit about internal resistance so am slightly confused by it all. so how would i work out this queston?? four identical cells, each of e.m.f 1.5V and internal resistance 0.1 ohms are connected in series. What current will this combination of cells drive through a bulb of resistance 2.0 ohms??

If working in series...

4 x 1.5v = 6v

(4 x 0.1ohm = 0.4 ohms) + bulb's 2 ohms

I=V/R

HTH

Reply 5

rainy_skye

OP

REME-Bod

If working in series...

4 x 1.5v = 6v

(4 x 0.1ohm = 0.4 ohms) + bulb's 2 ohms

I=V/R

HTH

ohhhh, i get it now. So its basically going through each section and then putting it all together into the equations of I=V/R
Thanx :smile:

Reply 6

REME-Bod

1

rainy_skye

ohhhh, i get it now. So its basically going through each section and then putting it all together into the equations of I=V/R
Thanx :smile:

Be aware that this is only the case for series ccts. The rules change if the cct is parallel or a combination.

Reply 7

Misogynist

18

Electro-motive force. Basically the voltage across a battery when no current is flowing through it.

Reply 8

andyj72

2

EMF => stands for electromotive force. it sint actually a force but the term use to describe the TOTAL charge flowing thru the whole/entire circuit Voltage = workdone/ charge. you should get full marks here.

so in other words the total work done to move total charge thru the entire circuit

hope it helps. use this and you will get full marks hopefully. i got an A in phy2 => electricity and thermal physics whichh was quite a while hehe

Reply 9

andyj72

2

Godsize

Electro-motive force. Basically the voltage across a battery when no current is flowing through it.

you can say this. but in an exam make this your seconfd answer cos you may not get a mark at all. to be on the safe side just put V=work done(forgot the letter)/Q

plz guys what is the letter? ive forgotten

Reply 10

andyj72

2

the working out is like this

E = emf
V= volts
IR = terminal pd
Ir = lost volts
R = resistance of bulb
r = internal resistance

Emf = terminal pd + lost volts

E = IR + Ir

1.5 *4 = 6v for emf

0.1 *4 = 0.4ohms internal resistance

2ohms for the resistance

6 = 2I +0.4I

6 = 2.4I

6/2.4 = I

I = 2.5A => current thru the circuit

i think im right but can someone correct me if im wrong.

Reply 11

Misogynist

18

andyj72

you can say this. but in an exam make this your seconfd answer cos you may not get a mark at all. to be on the safe side just put V=work done(forgot the letter)/Q

plz guys what is the letter? ive forgotten

I've done AS Physics and got a high A, Like 20 marks off 300 UMS :smile:

Reply 12

db

17

Steeeeevo

well EMF stands for Electromagnetic field (if you didnt know) but im not a physist so I cannt help you any more than that. sorry.

It's actually Electomotive Force

Reply 13

andyj72

2

Godsize

I've done AS Physics and got a high A, Like 20 marks off 300 UMS :smile:

hehe, you got higher than me but im still better than you :smile:

Reply 14

Comp_Genius

4

EMF is the electromotive force, which is the amount of energy a cell transfers to a charge carrier, defined as joules per coulomb. By analogy, it can be thought of as the amount of electrical force / pressure applied. EMF is different from potential difference, which is the amount of energy received by a coulomb of charge.

Reply 15

rubysolstice

andyj72

you can say this. but in an exam make this your seconfd answer cos you may not get a mark at all. to be on the safe side just put V=work done(forgot the letter)/Q

plz guys what is the letter? ive forgotten

V= P/I, you mean? E since it's energy (joules).

What is EMF??

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