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Physics internal resistance mcq help me please

question: the diagram shows a resistor of resistance R connected to a cell of emf E and internal resistance r. which of the following correctly shows the potential difference V across the terminals of the cell?

Answer: V=ER/(R+r)

this question is from jan 2014 ial unit 2 physics paper q10.

PLEASE HELP ME UNDERSTAND THIS AND HOW THE ANSWER WAS DERIVED!
THANKSSS!! <333
Reply 1
Original post by pointlessdoubts
question: the diagram shows a resistor of resistance R connected to a cell of emf E and internal resistance r. which of the following correctly shows the potential difference V across the terminals of the cell?

Answer: V=ER/(R+r)

this question is from jan 2014 ial unit 2 physics paper q10.

PLEASE HELP ME UNDERSTAND THIS AND HOW THE ANSWER WAS DERIVED!
THANKSSS!! <333


E = V + Ir
E = IR + Ir
E = I(R+r)
I = E/(R+r)

Voltage across the terminals of cell is the same as the voltage across the resistor
V = IR
V = E/(r+R) * R
V = ER/(R+r)
Original post by Dowel
E = V + Ir
E = IR + Ir
E = I(R+r)
I = E/(R+r)

Voltage across the terminals of cell is the same as the voltage across the resistor
V = IR
V = E/(r+R) * R
V = ER/(R+r)


how do u know that Voltage across the terminals of cell is the same as the voltage across the resistor ??
Original post by MARYAM1234567
how do u know that Voltage across the terminals of cell is the same as the voltage across the resistor ??


Hey, we can also solve this like this. So

E = V + ir and E= IR + ir

So based on this we get that V= IR
So since I= E/(R+r)
V = ER(R+r)


So basically we know that voltage is E.M.F minus lost volts. So based on the equation we know that the p.d across R is the voltage. It is the only resistor in the circuit so the entire voltage flows through it.
Hope u understand.

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