Physics NCERT Exemplar Solutions Class 12th Chapter Three

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Explanation- according to ohms law

I= $\frac{E+E}{R+r1+r2}$

The potential difference across terminal is

V=e-Ir= E- $\frac{2E}{R+r1+r2}$ r1=0

E= $\frac{2Er1}{R+r1+r2}$

1= $\frac{2r1}{R+r1+r2}$

R+r1+r2 = 2r1

R= r1-r2

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Explanation- when all resistance are in parallel

$\frac{1}{R_p}=\frac{1}{R_1}+\dots \dots \dots \dots ..+\frac{1}{R_n}$ by multiplying this equation by R_min we have

$\frac{R_{min}}{R_p}=\frac{R_{min}}{R_1}+\dots \dots \dots \dots ..+\frac{R_{min}}{R_n}$

But there exist a term in RHS $\frac{R_{min}}{R_{min}}=1$ and other terms are positive so we have

$\frac{R_{min}}{R_p}=\frac{R_{min}}{R_1}+\dots \dots \dots \dots ..+\frac{R_{min}}{R_n}$ >1

This shows that equivalent resistance is less than maximum resistance available.

But when all resistance are in series

R_s =R₁+R₂………R_n

here must be R_max value in RHS

R_s= R₁+……R_max+….R_n

And R_s> R_max

So equivalent resistance is less than R_max

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Explanation-

 total resistance = 2+8= 10 ohm

I= $\frac{6-4}{2+8}$ = 0.2A

The direction of flow of current is always from high potential to low potential

If VB $>$ VA

VB-4V-0.2 $*$ 8 = VA

V_B-V_A= 3.6V

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Explanation – in series combination of resistors current I =e/R+r

10I= $\frac{e}{R+\frac{r}{n}}$

$\frac{1+n}{1+\frac{1}{n}}$ $\Rightarrow$ 10 = ( $\frac{1+n}{1+n}$ )n $\Rightarrow$ n=10

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Explanation- according to the relation V=e-Ir and I=e/r+R

The graphical relation between voltage and resistance.

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Explanation- If the value of R is increased, the current through the wire will decrease which in turn decreases the potential difference across AB, and  hence potential gradient (k) across AB decreases.
Since, at neutral point, for given emf of cell, l increases as potential gradient (k) across AB has decreased because E' = kl
Thus, with the increase of l, which will result in increase in balance length. So, jockey J will shift towards B

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Explanation – power consumed through wire is P=V^2/R =I²R . for transmitting the power there are two types either current is large or voltage is less or vice versa. But when current in the circuit is higher then power loss is also higher . so we transmit the power through high voltage circuits.

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Explanation- Alloys are used for making standard resistance coil because they have low temperature coefficient of resistance with less temperature sensitivity. The alloys also have high resistivity and hence high resistance, because for given length and cross-section area of conductor .

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Explanation- For the selection of metal for wiring in home the main criterion are: the availability, conductivity and the cost of the metal. The Cu wires or Al wires are used  for wiring in the home. The main considerations are involved in this process are cost of metal and good conductivity of metal.