CBSE Class 12 · 2006 · All India · Current ElectricityShort Answer

WhatsApp Email

Draw a circuit diagram using a metre bridge and write the mathematical relation used to determine the value of an unknown resistance. Why cannot such an arrangement be used for measuring very low resistances?

Solution

A metre bridge is a Wheatstone bridge with a 1 m wire. With the known resistance

R

in one gap and the unknown

X

in the other, at the null point

\frac{R}{X} = \frac{ℓ}{100 - ℓ} \Rightarrow X = R \frac{100 - ℓ}{ℓ}

. For very small

X

the fixed end/contact resistances are no longer negligible compared with

X

, so the result is unreliable.

CBSE Class 12 Board · 2006 · All India · Subjective

Practise more: all CBSE board PYQs on Current Electricity →

More board questions on Current Electricity

An ammeter and a voltmeter are connected in series to a battery, their readings being $A$ and $V$ respectively. If a resistor is now connected in parallel with the voltmeter, then:
CBSE 2024View solution →
A galvanometer shows full-scale deflection for a current $I_{g}$ . With a shunt $S_{1}$ it becomes an ammeter of range $(0 - I)$ ; with a shunt $S_{2}$ its range becomes $(0 - 2 I)$ . Then $\frac{S _{1}}{S _{2}}$ is:
CBSE 2024View solution →
(i) Define the 'temperature coefficient of resistance' of a metal.
(ii) Show the variation of the resistivity of copper with a rise in temperature.
(iii) The resistance of a wire is $10 Ω$ at $2 7^{\circ} C$ . Find its resistance at $- 3^{\circ} C$ , given the temperatu …
CBSE 2024View solution →
A current of $0.8 A$ flows in a conductor of $40 Ω$ for 1 minute. The heat produced in the conductor will be:
CBSE 2023View solution →
A cell of EMF $E$ is connected across an external resistance $R$ . When a current $I$ is drawn from the cell, the potential difference across its electrodes drops to $V$ . The internal resistance $r$ of the cell is:
CBSE 2023View solution →
Define current density and relaxation time. Derive an expression for the resistivity of a conductor in terms of the number density of charge carriers and the relaxation time.
CBSE 2023View solution →