JEE Main 2020 · 7 January · evening · Single correct · +4 / −1
The figure gives experimentally measured B vs H variation in a ferromagnetic material. The retentivity, coercivity and saturation, respectively, of the material are :
- (a) 1.0 T, 50A/m and 1.5 T
- (b) 1.5 T, 50 A/m and 1.0 T
- (c) 1.5 T, 50 A/m and 2.0 T
- (d) 150 A/m, 1.0 T and 1.5 T
Answer and solution
Answer (a) 1.0 T, 50A/m and 1.5 T
Solution
Physics sir · 4 steps
Read the loop where it cuts each axis, then read its highest point. Three readings, three answers.
- Retentivity. Retentivity is the B left in the material when H is brought back to zero. The loop cuts the B-axis at 1.0 T, so retentivity is 1.0 T.
- Coercivity. Coercivity is the reverse H needed to bring B down to zero. The loop cuts the H-axis at -50 A/m, so coercivity is 50 A/m.
- Saturation. Saturation is where the curve flattens out and B stops growing. The tip of the loop sits about halfway between the 1.0 and 2.0 marks, so saturation is about 1.5 T.
- So. In order, the values are 1.0 T, 50 A/m and 1.5 T, which is option (a).
The idea to keep. Retentivity is the B-intercept (in tesla), coercivity is the H-intercept (in A/m), saturation is the flat top of the loop. Check the units before you match the numbers.
Answer from the NTA final answer key. Solution by PrepWiser.