CAPF AC 2025 Q107: Science & Technology – Physics
- (a) Gauss's law
- (b) Newton's law
- (c) Pascal's law
- (d) Ampere's law
Answer: (a) Gauss's law
Explanation
Law saying there are no magnetic monopoles
How to think: magnetic field lines always form closed loops, so there is never a single isolated north or south pole.
The law that says this is Gauss's law for magnetism: the net magnetic flux through any closed surface is zero.
| Law | What it says |
|---|---|
| Gauss's law (magnetism) | No magnetic monopoles; ∮B·dA = 0 |
| Newton's law | Laws of motion and gravitation |
| Pascal's law | Pressure in a fluid is transmitted equally |
| Ampere's law | Magnetic field around a current |
Cutting a bar magnet only gives two smaller magnets, each with both poles.
Bank key corrected: the stored key was (c) Pascal's law; the right answer is (a) Gauss's law.
Answer: (a) Gauss's law.
Why each option is right or wrong
- (a) CORRECT. Gauss's law for magnetism says magnetic monopoles do not exist.
- (b) Incorrect. Newton's laws deal with motion and gravity.
- (c) Incorrect. Pascal's law is about pressure in fluids.
- (d) Incorrect. Ampere's law links current and magnetic field, not monopoles.
Key point
Maxwell's equations: Gauss for electricity (flux = q/ε₀), Gauss for magnetism (flux = 0, no monopoles), Faraday (induction), Ampere-Maxwell (current and changing E).
Remember
Gauss's law for magnetism: no monopoles, net flux zero.
Common mistakes
- Choosing Ampere's law because it is the best-known magnetism law.
- Picking Pascal's law because the name appears in many science questions.
- Thinking a magnet can be cut to isolate a single pole.
Exam tip
Educated guess: Newton and Pascal are famous for non-magnetic laws, so only Gauss and Ampere are in the running. Ampere's law gives a field from a current, so Gauss's law is the one about poles.
Sources
- NCERT Class XII Physics, Part I, Chapter 5 (Magnetism and Matter: Gauss's law for magnetism)
- David J. Griffiths, Introduction to Electrodynamics, chapter on Magnetostatics (the divergence of B is zero)