Question

The small box provided contains a cell of emf

E

and internal resistance

r

. Using this cell, an ammeter

(with negligible resistance), a variable (but known) resistance (

R

) and a plug key connect the circuit as

shown below.

Note

the meter polarity.

(a)

Does it matter in what order the components are connected? Explain.

(b)

In this experiment

I

is the dependent and

R

is the independent variable. Is this correct? Explain.

(c)

(d)

1

1

r

R

I





E

E

Write down the equation for

E

in terms of the current,

I

, the external resistance,

R

, and the

internal resistance of the cell,

r

.

(E2.1)

Show that equation (E2.1) can be rearranged into a form suitable for plotting a straight-line

graph:

Answer 1

As here question is referring a diagram but it is not attached. And question is also very splitted way, so it is not clear, hence i am taking the approximation.

As per the question,

Emf of cell = E

Internal resistance = r

Resistance of variable resistor = R

equivalent resistance of the circuit = R+r

current in the circuit $(I)=\frac{E}{r+R}$

Potential developed across the internal resistance $E_r=rI = \frac{rE}{R+r}$

Potential developed across the resistance R,

$V= IR = \frac{ER}{r+R}$

And net emf across the battery = $V_{net}=E-\frac{Er}{R+r}= \frac{ER+Er-Er}{R+r}=\frac{RE}{R+r}$