ICSE.X.PHYSICS. 8. CURRENT AND ELECTRICITY

Calculate the area of cross-section of a wire of length 80 cm, if its resistance is 20 Ω and resistivity of the material of the wire is 1.8 × 10⁻⁶ Ω-m.

• 7.2×10⁻⁸ m²

• 1.2×10⁻⁸ m²

• 5.0×10⁻⁸ m²

• 9.0×10⁻⁸ m²

Calculate the resistance of a copper wire 1.5 km long and 0.4 mm thick if the resistivity of copper is 1.7 × 10⁻⁸ Ω-m.

• 202.84 Ω

• 150.50 Ω

• 180.30 Ω

• 220.10 Ω

The resistance of a metal wire of length 2 m is 50 Ω at 20°C. If the diameter of the wire is 0.4 mm, calculate the resistivity of the metal at this temperature.

• 3.14 × 10⁻⁸ Ω-m

• 1.57 × 10⁻⁸ Ω-m

• 6.28 × 10⁻⁸ Ω-m

• 2.00 × 10⁻⁸ Ω-m

A length of wire having resistance 10 Ω is drawn out, so that its length is increased by 50 per cent. Calculate the resistance of the wire in its new shape and size.

• 22.5 Ω

• 15 Ω

• 30 Ω

• 12.5 Ω

In parallel combination of resistances: (a) p.d. is same across each resistance (b) total resistance is increased (c) current is same in each resistance (d) all above are true.

• p.d. is same across each resistance

• total resistance is increased

• current is same in each resistance

• all above are true

In series combination of resistances: (a) p.d. is same across each resistance (b) total resistance is reduced (c) current is same in each resistance (d) all above are true.

• p.d. is same across each resistance

• total resistance is reduced

• current is same in each resistance

• all above are true

Two unequal resistances are connected in parallel across a cell. Which of the following statements is true?

• Current flowing through smaller resistance is higher.

• Current flowing through larger resistance is higher.

• Current flowing through both the resistances is equal.

• Current can be higher in any resistance depending on the emf of the cell.

Ohm’s law defines the relationship between:

• Current and electric charge

• Potential difference and resistance

• Resistance and current

• Current and potential difference

Electrical resistance is the ratio of:

• Potential difference to electric current

• Electrical energy to current

• Electric current to potential difference

• Electric charge to potential difference

Keeping the p.d. constant, the resistance of a circuit is halved. The current will become:

• Half

• One-fourth

• Four times

• Double