Resistivity and Kirchhoff laws

The unit of resistivity is

• Ω/m

• Ω/m²

• Ω.m

• Ω.m²

The nichrome wire has a cross-sectional area of 1.3 × 10^–7 m² . Resistivity of nichrome = 1.1 × 10^–6Ωm. If the measured resistance is 53 Ω, what is the length of the wire ? Show your calculations on the paper.

A copper wire of length 2.5 m and 2.76 × 10^-4 m radius has a resistivity (ρ) of 1.7x10^-8Ωm. What is the resistance of the wire? Show your calculations on the paper.

A cylindrical conductor of length l, diameter D, and resistivity ρ has a resistance R. What is the resistance of another cylindrical conductor of length l, diameter D/2 , and resistivity ρ? Show your reasoning on the paper.

• 8R

• 4R

• 2R

• R

A wire of uniform diameter 0.28mm and a length of 1.50m has a resistance of 45Ω. It's resistivity is (show your process on the paper)

• 2.2 x 10^-8Ωm

• 36 Ωm

• 1.8 x 10^-6Ωm

• 3.4 x 10^-7Ωm

Two resistors R1 and R2 are made of wires of the same material. The wire used for R1 has half the diameter and is twice as long as the wire used for R2.

What is the value of the ratio resistance of R1 / resistance of R2?

• 8

• 4

• 1

• 0.5

1. Kirchhoff's junction rule is a reflection of

• Conservation of current density vector

• Conservation of charge and no accumulation of charge at the the junction

• the momentum with which a charged particle approaches a junction is unchanged as the charged particle leaves the junction

• Conservation of energy

What is the power of a 3V light bulb with 20 A running through it? (Show your reasoning on the paper)

• 0.15W
• 6W
• 60W
• 6.67W

The figure below shows currents in a part of electric circuit. The current i is ________ .

• 2 A

• 1.3 A

• 1.7 A

• 1 A

What is the correct expression for the currents at the following node?

• I₁+I₂=I₃+I₄

• I₁=I₂+I₃-I₄

• I₁+I₃=I₂+I₄

• I₁-I₃=I₂-I₄