Physics M.C.Q (1 Marks)

The conductors which obey $Ohm’s$ law are called Ohmic conductors. The linear relationship between voltage and current for these conductors hold good. The resistance $(\text{R}=\frac{\text{V}}{\text{I}})$is independent of the current through the conductor. The magnitude of current changes linearly with voltage. Hence the $V-I$ graph for ohmic conductors is a straight line passing through the origin.

A wire wound resistor is an electrical passive component that limits current. The resistive element exists out of an insulated metallic wire that is winded around a core of non$-$conductive material. The wire material has a high resistivity, and is usually made of an alloy such as Nickel$-$chromium $($Nichrome$)$ or a copper$-$nickel$-$manganese alloy called Manganin. Common core materials include ceramic, plastic and glass. It has a lower order of stability and reliability is not true for wire wound resistor.

p-n junction diode consists of $p-$type and $n-$type semiconductors. The $V-I$ relationship is non-linear. When a voltage is applied across junction, very little current flows for the fairly high negative voltage and a current begins to flow for much smaller positive $($forward$)$ bias. The magnitude of variation depends upon the sign of potential difference applied across it.

The equation $\rightarrow ∑e = ∑IR$ is applicable to Kirchhoff’s second law. This law is also known as Kirchhoff’s loop rule. This expression tells us that in a closed loop, the algebraic sum of the emfs is equal to the algebraic sum of the products of the resistance and currents flowing through them.

The current that flows from a point at the higher $($positive$)$ potential to a point at lower $($negative$)$ potential is called conventional current. The direction of motion of positive charges is taken as the direction of electric current.

$\text{E.m.f}$ of a cell is defined as the maximum potential difference across the cell when no current flows through the circuit.

Wheatstone bridge is an arrangement of four resistors $\text{P, Q, R,}$ and $S$, such that if we know the value of the resistances of any three of them, we can obtain the value of fourth unknown resistance. Therefore, there are $4$ resistances in a Wheatstone bridge.

Kirchhoff’s $2^{nd}$ year is applied in a closed loop. Kirchhoff’s $2^{nd}$ law supports the law of conservation of energy. This means that energy is neither created nor destroyed in the closed loop. Whatever energy enters the loop, same amount leaves the loop.

Key concept: In this problem, the concept of balanced Wheatstone bridge is to be used.
Condition of balanced wheat stone bridge: The bridge is said to be balanced if the ratio of the resistances in same branch is equal $\frac{R}{S}=\frac{I_1}{\left(100-I_1\right)}$.
Wheatstone bridge is an arrangement of four resistances which can be used to measure one unknown resistance of them in terms of rest.
The percentage error in $R$ can be minimised by adjusting the balance point near the middle of the bridge, i.e., when is close to $50 \ cm $. This requires a suitable choice of $S$.
Since, $\frac{R}{S}=\frac{I_1}{\left(100-I_1\right)}$
Since here, $R: S=2.9: 97.1$
Then the value of $S$ is nearly $33$ times to that of $R$. In order to make this ratio $1: 1$, it is necessary to reduce the value of $S$ nearly $\frac{1}{33}$ times, i.e., nearly $3 \Omega$.

emf of secondary cell $= I r l$
where
$I -$ current in the main circuit from battery.
$r -$ resistance per unit length of wire.
$l -$ balancing length.

$\phi$ Kirchhoff's Junction Law follows from conservation of charge.
$\phi$ Kirchhoff's loop law fallows from conservation nature of electric field.

Most of the metals obey Ohm’s law and they are called ohmic conductors. Whereas semiconductors are non$-$ohmic. Nichrome metal is an ohmic conductor in which the $V-I$ characteristic has a straight line passing through the origin.

If we add two non ideal batteries in series then.
so in case $(a)$ the equivalent $e.m.f.$ may be larger than either of two $e.m.f.$, but in case $(b)$ the equivalent $e.m.f.$ may be smaller than either of two $e.m.f.$
In series total resistance is always greater than individual resistance, whether batteries are connected in any way
[i.e. either according to case $(a)$ or case $(b)].$

The drift velocity of electrons decreases when the length of the conductor is increased.
Drift velocity $=\frac{\text{Potentialdifference}}{\text{(numberofelectrons×chargeofelectron×lengthofconductor×density).}}$