Question

A wire of resistance 5 ohms is stretched such that longitudinal strain is $200 \%$.The new resistance in ohms is

• A. 10
• B. 25
• C. 30
• D. 45

Answer 1

The Correct Option is D

Here, $R = 5 \, \Omega$,
or $ R = \frac{\rho l}{A} = \frac{\rho l^2}{V} \, \, (\because \, V= Al)$
On stretching, longitudinal strain,
$ \frac{\Delta l}{l} = 200 \% = 2$
$ \Delta l = 2 l $ ....(i)
New length of wire $I'= I + \Delta l = 3 l$ (Using (i))
or, $R' = \frac{\rho l'^2}{V} = \frac{\rho(3l)^2}{V} = 9 \times 5 = 45 \, \Omega$

Answer 2

Ans. R=V/I is the formula for resistance. Resistance is the amount of resistance anything applies to the passage of electric current. An electrical component in a circuit known as a resistor delivers a certain level of resistance. Resistance is a characteristic of materials that permits the flow of electric current. Resistance obviously opposes the current flow. Additionally, ohms (Ω), represented by the Greek capital letter omega, is the SI unit of resistance.

• The movement of electrons is an electrical current.
• Electrical resistance is a measurement of a device's resistance to the passage of electricity through it.

Ohm's law can be used to calculate the electrical resistance of a given system. Ohm's law is a well-known practical law of circuit physics. According to Ohm's law, the current flowing through a circuit is directly proportional to the voltage applied across it and inversely proportional to the resistance provided by the wire, assuming that the temperature remains constant. Ohm's law is expressed as a formula.

V = IR

R = V/I

• V denotes the applied voltage.
• I represent the current.
• R denotes electrical resistance.

If voltage and current are known, the above formula can be used to calculate the electrical resistance.

A conductor's electrical resistance is determined by the following factors:

• The cross-sectional area of the conductor
• The length of the conductor
• The material of the conductor and the temperature

The electrical resistance is proportional to the length of the conductor (L) and inversely proportional to the cross-sectional area (A). It is denoted by the following relationship.

R = ρL/A

where ρ is the material's resistivity (measured in ohm meter)

The ability of a material to resist flowing electric current is measured qualitatively as resistivity. Insulators, by definition, have higher resistivity than conductors. For comparison, the resistivities of a few materials are listed below. Materials with a low resistivity value conduct electricity very well.

Silver – 1.00×10⁻⁸

Copper – 1.68×10⁻⁸

Aluminium – 2.82×10⁻⁸

Wood – 1.00×10¹⁴

Air – 2.30×10¹⁶

Teflon – 1.00×10²³