Resistance : Factors and Cases | Electricity | Assessment | English | Grade 10

Resistivity depends upon _______ of the wire and it's SI unit is _____ .

• material of the wire; Ωm

• length of the wire; Ω

• material of the wire; Ω

• cross sectional area and length of the wire; Ωm

Answer explanation

Resitivity depends on the material of the wire and it's SI unit is Ωm.

Choose the correct statement: Assertion (A): Current is decreased when length of the wire is increased. Reason (R): Resistance in a circuit is directly proportional to the length of the wire.

• Both A and R are true and R is the correct explanation of A

• Both A and R are true but R is not the correct explanation of A

• A is true but R is false

• Both A and R are false

Answer explanation

When length of the wire is increased the resistance is increased. Current has to face more resistance in the wire. When resistance increases, current decreases.

What will happen to the resistance if the radius of the wire is made twice and length becomes half?

• Resistance will become 4 times

• Resistance will become 8 times

• Resistance will become half

• Resistance will become 1/8 times

Answer explanation

Length of the wire = l Cross sectional area = A = πr² where r is the radius R₁ = ρl/A = ρl/πr² R₂ = ρl/π2(2r)² R₂/R₁ = 1/8

The MCBs are connected in series with the whole power supply coming to your house because _______ .

• MCBs has copper wire inside them

• MCBs enhance voltage supply

• all the current flows through the MCB. In case of short circuit it stops the supply there only

• the circuit is sensitive to the electric current. It get discharged when more than the rated current flows through it.

Answer explanation

MCBs are connected in series so that all the current pass through it.

Choose the odd one out

• 1/R = 1/R₁ + 1/R₂ + 1/R₃

• V is constant

• I = I₁ + I₂ + I₃

• V = V₁ + V₂ + V₃

Answer explanation

First three options show the relation around the parallel circuit but last one shows the relation of series circuit.

Calculate the current in the circuit.

• 6 A

• 1.5 A

• 1 A

• 4.5 A

Answer explanation

We have four resistances: R₁ = 3 Ω R₂ = 2 Ω R₃ = 4/3 Ω R₄ = 4 Ω Equivalent of the parallel circuit 1/Rₐ = 1/R₃ + 1/R₄ = 3/4 + 1/4 = 1 Rₐ = 1 Ω Equivalent R of the series circuit: Rₑ = R₁ + R₂ + Rₐ = 3+2+1 = 6 Ω Current (I) = V/Rₑ = 9/6 = 1.5 A