✓ Board-verified
Physics · 2025 · 3 marks
CBSE 2025 · Region 5 · Set 2 · Q27
(a) Use Ampere's law to derive the expression for the magnetic field due to a long straight current carrying wire of infinite length. (b) Why is…
(a)
Use Ampere's law to derive the expression for the magnetic field due to a long straight current carrying wire of infinite length.
(b)
Why is Ampere's law used for the derivation in (a) above and not Biot-Savart's law? Explain.
Marking-scheme solution
(a)
Consider an Amperian loop of radius R around the wire carrying current I.
$\displaystyle \oint \vec{B} \cdot d \vec{l}=\mu_{0} i$
$\displaystyle B \times 2 \pi r=\mu_{0} i$
$\displaystyle B=\frac{\mu_{0} i}{2 \pi r}$
(b)
The expression for the magnetic field due to a long straight current carrying infinite wire can be obtained easily using Ampere's circuital law, whereas Biot-Savart's law requires lengthy calculation.
All Moving Charges and Magnetism questions2025 question paperNCERT solutions: Moving Charges and MagnetismPractice Moving Charges and Magnetism →
More from Moving Charges and Magnetism
- A 2.0 cm segment of wire, carrying 5.0 A current in positive y-direction lies along y -axis, as shown in the figure. The magnetic field at a point (3…2024
- Two thin long parallel wires A and B are separated by a distance r and carry current I each in the same direction. The force per unit length exerted…2023
- Derive an expression for the magnetic field B, due to a circular coil of N turns, each of radius r carrying current I, at a distance ' x ' from the…2026
- Assertion: A proton and an electron enter a uniform magnetic field B with the same momentum p such that p is perpendicular to B. They describe…2024
- Beams of electrons and protons move parallel to each other in the same direction. They2023
- (i) A particle of mass m and charge q is moving with a velocity v in a magnetic field B as shown in the figure. Show that it follows a helical path.…2024
- Figure shows a narrow beam of electrons entering with a velocity of 3 × 10^7 m / s, symmetrically through the space between two parallel horizontal…2026
- A particle of mass m and charge q moving with a uniform velocity v=v_0 x i+v_0 y j enters a region with a magnetic field B=B_0 j. After some time, an…2023
CBSE Class 12 Physics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.