# OCR G482 emf

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#1
Hi, I'm having a bit of a struggle with emf and internal resistance and wondered if anyone had some helpful material I could have a look at. I'm also trying to answer the textbook question below, any help would be appreciated, thanks.

Explain the difference between emf and terminal p.d.
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5 years ago
#2
(Original post by AidanP96)
Hi, I'm having a bit of a struggle with emf and internal resistance and wondered if anyone had some helpful material I could have a look at. I'm also trying to answer the textbook question below, any help would be appreciated, thanks.

Explain the difference between emf and terminal p.d.
Electrons are fundamental force carriers. i.e. they have the property of exerting a force over a distance which attracts oppositely charged particles (protons) and repel like charges (other electrons).

Electro Motive Force (E.M.F.) does what is say's in the name: It's a large collection of charged particles (electrons or protons) whose individual electric forces sum to produce a large force able to exert a 'pressure' on mobile electrons within a conductor.

The ability to generate and distribute a force also has the ability (potential) to perform work and E.M.F. is measured as a voltage. i.e. potential for doing work.

EMF is a collective term associated with processes for generating that electric charge force: battery cells, dynamos, photo-voltaic cells etc.

Potential difference p.d. also does what it says in the name. It implies a difference in potential for doing work as measured between two different places.

This manifests itself when a current (movement of electrons) passes through a resistance. The electrons give up some of their potential energy as a result of that resistance in the form of heat.

That means the original EMF (measured in volts) has lost some of it's potential energy as a result of the work done in moving through the resistance.

The difference in potential energy measured on entry with the resistance and on exit of that resistance is also stated as a voltage but this time the voltage is the 'lost' potential energy across that resistance.

i.e. electrons have lost energy potential, hence 'potential difference'.

You should now see that all primary cells have the ability to produce a large electric pressure (bulk charged particles) measured as an E.M.F. and also that the cell has an internal resistance where the original E.M.F. must give up some of it's energy to that internal resistance as heat.

The loss is a potential difference as measured at the battery terminals connecting to the outside world.
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