HC Verma: Concepts of Physics - Volume 2 Magnetic Field Pages 230-234: Q23 Solution: A metal wire PQ of mass 10 g lies at rest on two horizontal…

QPages 230-234: Q23: HC Verma: Concepts of Physics - Volume 2 Magnetic Field Pages 230-234: Q23 Solution: A metal wire PQ of mass 10 g lies at rest on two horizontal…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently fail to convert the rail separation from centimeters to meters before applying the magnetic force formula $F = i l B$, leading to a result that is off by a factor of 100. Always ensure all linear dimensions are in SI units (meters) to match the Tesla and Newton definitions.

A metal wire PQ of mass 10 g lies at rest on two horizontal metal rails separated by 4.90 cm figure). A vertically-downward magnetic field of magnitude 0.800 T exists in the space. The resistance of the circuit is slowly decreased and it is found that when the resistance goes below

20.0 \ \Omega

, the wire PQ starts sliding on the rails. Find the coefficient of friction.

Step-by-Step Verified Solution

**Answer:**

\mu = 0.12

. **Step-by-Step Explanation:** The wire starts sliding when the magnetic force exceeds friction:

i l B = \mu m g

. At

R = 20\ \Omega

i = V/R = 6/20 = 0.3 \text{ A}

\mu = \frac{i l B}{m g} = \frac{0.3 \times 0.049 \times 0.8}{0.01 \times 9.8} = 0.12

QPages 230-234: Q23: HC Verma: Concepts of Physics - Volume 2 Magnetic Field Pages 230-234: Q23 Solution: A metal wire PQ of mass 10 g lies at rest on two horizontal…

Step-by-Step Verified Solution

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