The known forces of nature can be divided into four classes, viz., gravity, electromagnetism, weak nuclear force and strong nuclear force. With reference to them, which one of the following statements is not correct?
Contents13
- AGravity is the strongest of the four
- BElectromagnetism acts only on particles with an electric charge
- CWeak nuclear force causes radioactivity
- DStrong nuclear force holds protons and neutrons inside the nucleus of an atom
Show answer
Answer: (A) Gravity is the strongest of the four
The question asks which statement is NOT correct.
Option (a) says 'Gravity is the strongest' — this is WRONG, and therefore the correct answer.
Gravity is actually the WEAKEST of the four fundamental forces — it is about 10^36 times weaker than the strong nuclear force!
A simple demonstration: when you rub a comb on your shirt and it lifts a piece of paper off a desk, the electromagnetic force of that tiny comb is overcoming the gravitational pull of the entire Earth on that paper.
The other three statements are correct:
(b) Electromagnetism acts only on electrically charged particles.
(c) Weak nuclear force is responsible for radioactive decay (beta decay).
(d) Strong nuclear force is what holds protons and neutrons together inside the nucleus, overcoming the electromagnetic repulsion between positively charged protons.
Gravity is actually the weakest of the four fundamental forces, about 10^36 times weaker than the strong nuclear force, despite being the most familiar to us.
This question tests basic physics knowledge that connects to nuclear energy topics, since understanding nuclear forces is essential for comprehending how nuclear reactors and atomic structure work.
Four Fundamental Forces of Nature
Science And Technology gravity electromagnetism weak nuclear force strong nuclear force
Four Fundamental Forces: Strength Hierarchy & UPSC Traps
Gravity is the weakest force, not strongest — 10^36 times weaker than strong nuclear force
Strong nuclear force is strongest, holds nucleus together despite proton repulsion
Electromagnetic force acts only on charged particles, second strongest
Weak nuclear force causes radioactive decay, third strongest
Why This Matters
The fundamental forces govern all interactions in the universe. UPSC frequently tests their relative strengths and specific roles — the biggest trap is assuming gravity is strong because we experience it daily.
Force Comparison
Force | Relative Strength | Range | Acts On | Key Role |
|---|---|---|---|---|
Strong Nuclear | 1 (strongest) | 10^-15 m | Quarks, nucleons | Holds nucleus together |
Electromagnetic | 10^-2 | Infinite | Charged particles only | Chemical bonds, light |
Weak Nuclear | 10^-13 | 10^-18 m | All particles | Radioactive decay |
Gravity | 10^-36 (weakest) | Infinite | All mass/energy | Planetary motion, tides |
Daily Life Examples
Comb lifting paper: Electromagnetic force of tiny comb overcomes Earth's entire gravitational pull
Nuclear power: Strong force binding energy released when nucleus splits
Radio waves: Electromagnetic force creates and propagates all forms of light
Carbon-14 dating: Weak force causes radioactive decay used in archaeology
Question Analysis
This PYQ tests the strength hierarchy misconception. Statement A claims gravity is strongest — completely wrong since gravity is the weakest force. The other three statements correctly describe electromagnetic selectivity, weak force radioactivity, and strong force nuclear binding.
Trap: Assuming gravity is strong because we feel it daily — it's actually the weakest by far
Trap: Confusing strong nuclear force with weak nuclear force roles
Trap: Thinking electromagnetic force acts on all particles — it acts only on charged particles
Trap: Forgetting that weak force, despite its name, is stronger than gravity
Nuclear Forces: Strong vs Weak
Science And Technology strong nuclear force weak nuclear force nucleus radioactivity
Nuclear Forces: How They Hold Atoms Together & Cause Decay
Strong nuclear force binds protons and neutrons in nucleus, overcomes electromagnetic repulsion
Weak nuclear force causes radioactive decay, converts neutrons to protons in beta decay
Strong force range: 10^-15 m, weak force range: 10^-18 m — both very short
The Nuclear Challenge
Inside the nucleus, positively charged protons should repel each other violently due to electromagnetic force. The strong nuclear force overcomes this repulsion at extremely short distances, binding protons and neutrons together.
How Strong Force Works
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Protons Repel**
Electromagnetic force pushes positive charges apart`"]
s2["`**Strong Force Activates**
At distances < 10^-15 m, strong force dominates`"]
s3["`**Quarks Exchange Gluons**
Force carriers bind quarks within protons/neutrons`"]
s4["`**Nucleus Stays Bound**
Strong force wins over electromagnetic repulsion`"]
s1 --> s2
s2 --> s3
s3 --> s4Strong vs Weak Nuclear Forces
Aspect | Strong Nuclear Force | Weak Nuclear Force |
|---|---|---|
Primary Role | Binds nucleus together | Causes radioactive decay |
Typical Process | Holds protons + neutrons | Beta decay (n → p + e + ν) |
Force Strength | Strongest of all four | 10^11 times weaker than strong |
Range | ~10^-15 m (nuclear size) | ~10^-18 m (much shorter) |
Force Carriers | Gluons | W and Z bosons |
UPSC Example | Why nucleus doesn't fly apart | Why Carbon-14 decays to Nitrogen-14 |
Trap: Mixing up which force does what — strong binds, weak decays
Trap: Thinking weak force is weaker than gravity — it's actually 10^23 times stronger than gravity
Trap: Assuming nuclear forces have long range like gravity/electromagnetic — both are extremely short-range
Electromagnetic Force & Charged Particles
Science And Technology electromagnetism electric charge
Electromagnetic Force: Why It Only Acts on Charged Particles
Acts only on electrically charged particles — neutral particles feel no electromagnetic force
Second strongest force, creates chemical bonds and all forms of light
Force carrier is photon, has infinite range like gravity
Charge Selectivity
Unlike gravity (which acts on all mass) and nuclear forces (which act on specific particles), electromagnetic force is highly selective — it only affects particles with electric charge: electrons (-), protons (+), and ions.
What Electromagnetic Force Creates
Chemical bonds: Electrons attracted to protons form atoms and molecules
Light and radio waves: Accelerating charges create electromagnetic radiation
Electricity and magnetism: Moving charges create magnetic fields, changing fields create electric fields
Friction and contact forces: Electromagnetic repulsion between electron clouds
All everyday forces except gravity are ultimately electromagnetic
Particles & Electromagnetic Force
Particle Type | Electric Charge | Feels EM Force? | Example Interaction |
|---|---|---|---|
Electron | Negative (-e) | Yes | Attracted to protons, repelled by other electrons |
Proton | Positive (+e) | Yes | Attracted to electrons, repelled by other protons |
Neutron | Zero (neutral) | No | Passes through matter easily, no EM interaction |
Photon | Zero (neutral) | No* | *Carries EM force but has no charge itself |
Neutrino | Zero (neutral) | No | Passes through Earth without EM interaction |
Trap: Assuming EM force acts on all particles — neutrons and neutrinos are immune
Trap: Confusing photons (EM force carriers) with charged particles — photons have zero charge
Trap: Thinking gravity acts only on charged particles — gravity acts on all mass/energy