CBSE Class 10 Science 2025: question 32

Hints

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Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

1. Given: $r=0.01\text{cm}=0.01\times 10^{-2}\text{m}=1\times 10^{-4}\text{m}$, $R=7\Omega$, $\rho =44\times 10^{-6}\Omega \text{m}$.

   ½ mark

2. Area of cross-section: $A=\pi r^2=\frac{22}{7}\times (10^{-4}{)}^2{\text{m}}^2=\frac{22}{7}\times 10^{-8}{\text{m}}^2$.

   ½ mark

3. $R=\rho \frac{l}{A}\Rightarrow l=\frac{RA}{\rho }$

   ½ mark

4. $l=\frac{7\times \frac{22}{7}\times 10^{-8}}{44\times 10^{-6}}=\frac{22\times 10^{-8}}{44\times 10^{-6}}$

   1 mark

5. $l=0.5\times 10^{-2}\text{m}=0.005\text{m}$ (= 0.5 cm).

   ½ mark

Answer: l = 0.5 × 10⁻² m = 0.005 m (0.5 cm)

Revise the chapter

• Chapter: Electricity (notes, formulas, where marks are lost and every past question)