Which of the following is true for cathode ray? — Atomic Structure Chemistry Question

💡 Solution & Explanation

### Step 1 - Nature of Cathode Rays Cathode rays are streams of fast-moving electrons emitted from the cathode in a gas discharge tube. They have: * Mass: $m_e \approx 9.1 \times 10^{-31}$ kg * Charge: $-e \approx -1.6 \times 10^{-19}$ C * Travel in straight lines (in absence of fields) * Are deflected by both electric and magnetic fields ### Step 2 - Evaluate Option (A) **"Not deflected by magnetic field"** — INCORRECT. Moving charges experience Lorentz force in a magnetic field: $$\vec{F} = q(\vec{v} \times \vec{B})$$ Cathode rays (electrons) ARE deflected by magnetic fields. ### Step 3 - Evaluate Option (B) **"Electromagnetic wave"** — INCORRECT. Cathode rays consist of material particles (electrons) with mass and charge. Electromagnetic waves (light, X-rays, gamma rays) are massless photons. Completely different. ### Step 4 - Evaluate Option (C) **"Emits X-ray when strikes a metal"** — CORRECT. When high-energy electrons (cathode rays) suddenly decelerate upon hitting a heavy metal target (tungsten), their kinetic energy converts to high-energy, short-wavelength electromagnetic radiation — X-rays (Bremsstrahlung radiation). This is the fundamental principle of X-ray generation. ### Step 5 - Evaluate Option (D) **"Consists of all negative particles in atoms"** — INCORRECT. Cathode rays consist exclusively of **electrons**. Saying "all negative particles" is imprecise — other negative particles exist (negative pions, muons, etc.) but are not cathode ray constituents. $$\text{Correct Option: } \boxed{\text{C}}$$