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emf and voltage
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I've watched 8.02x videos, tried reading from book, but still couldn't understand the difference between voltage and emf. I am stuck and helpless. Help me, kind people.

I understood electric field, potential, capacitance, and dielectrics very well but when circuits came they confused me. Could anyone please guide me?

Pic unrelated.
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emf is open loop voltage
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>>7807347
You mean emf is the potential difference between the terimals of a battery not connected to anything?

Also, how does a potential differnce exists across the terminals?
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>>7807364
yes
charge separation, result of chemical reaction
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>>7807401
I have one more question. When we add some device with some resistance to a circuit powered by a battery, why is there a decrease in it's emf which we then later call it potential? Book says it's because of internal resistance, but why that internal resistance isn't there when the battery is not connected to anything?
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>>7807428
>why is there a decrease in it's emf
There isn't. The emf is the unloaded potential difference while the terminal voltage decreases with increasing load current. Internal resistance and external load resistor form a voltage divider.
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>>7807301
When a charged particle passes through a power supply, it gains energy. The energy gained from passing through is the terminal pd.
When it passes through the power supply, it encounters resistance (aptly named internal resistance). This resistance causes the charge carrier to loose energy.
It constantly looses energy as it passes through the supply but it helps to think of it like passing through the whole power source gaining energy, then passing through an internal resistor, then leaving the supply. The emf is the total energy the charged particle gains from the power supply. Is it the energy it receives from the power supply. The terminal pd is the net energy gained, taking account of this internal resistance.
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>>7807966
I tried to draw what I described
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>You mean emf is the potential difference between the terimals of a battery not connected to anything?
This is wrong
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>>7807301
And if you mean what is voltage, it is the energy transferred, per coulomb, when the coulomb moves from an area of higher electrical potential energy to an area of lower potential energy.
Its exactly how like when something falls, it moves from an area of higher gravitational potential energy to an area of lower gravitational potential energy. You could say that if 1kg falls, and transfers 2J of energy, its pd is 2J/kg (the mass version of the electrical volt).
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>>7808011
the 2J being transferred to kinetic in the case of gravity may I add, in terms of electrical potential energy it may be transferred to heat through resistance or light in a LED etc
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>>7807966
>emf is the total energy
No, it is the potential, energy/charge.
emf should be called source voltage
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>>7808055
>The emf is the total energy the charged particle gains from the power supply
How is that not
>The emf is the total energy the charged particle gains from the power supply
apart from taking out particle (which to me makes it harder to understand (which then once you understand you can realise that it needs to go yourself))
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>>7808089
I meant >emf is the total energy on line 1 :s