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Predicted Questions with Model Answers
Q1 (5 marks — 50 words): What is MRI? How does it differ from CT scan and X-ray in its working principle and clinical applications?
Model Answer:
MRI (Magnetic Resonance Imaging) uses a 1.5–3 Tesla magnetic field and radiofrequency pulses to image hydrogen atoms in body tissues — no ionising radiation. Best for soft tissues (brain tumours, MS, ligaments). CT scan uses multiple X-ray beams reconstructed into 3D slices — good for bone, chest, internal organs; moderate radiation dose. X-ray uses single X-ray beam — quick, low cost, ideal for bone fractures and chest infections; highest radiation per study area.
Q2 (5 marks — 50 words): What is total internal reflection? State the conditions for TIR and give two applications.
Model Answer:
Total Internal Reflection (TIR) occurs when light travels from a denser to a rarer medium and the angle of incidence exceeds the critical angle (θc). Conditions: (1) light must travel from optically denser to rarer medium; (2) angle of incidence > θc. Critical angle for glass ≈ 42°. Applications: (1) Optical fibres — light signals transmitted with negligible loss in telecommunications and endoscopy; (2) Diamond brilliance — n=2.42 gives θc=24.4°, causing multiple internal reflections.
Q3 (5 marks — 50 words): Explain electromagnetic induction. State Faraday's laws and mention two practical applications.
Model Answer:
Electromagnetic induction (Faraday, 1831): A changing magnetic flux through a closed circuit induces an EMF. Faraday's Laws: (1) EMF is induced whenever magnetic flux changes; (2) magnitude of induced EMF equals the rate of change of flux. Lenz's Law: Induced current opposes the change causing it (energy conservation). Applications: (1) AC Generator — rotating coil in magnetic field generates AC electricity powering homes and industries; (2) Transformer — changes voltage levels for efficient long-distance power transmission.
Q4 (5 marks — 50 words): What is the Doppler effect? State two applications in science and technology.
Model Answer:
The Doppler Effect is the apparent change in frequency of a wave when the source and observer are in relative motion. Frequency appears higher when source approaches and lower when it recedes. Formula: f' = f(v ± vo)/(v ∓ vs). Applications: (1) Doppler radar — meteorologists measure storm wind speeds by detecting frequency shift in radar echoes from rain droplets, improving cyclone warnings; (2) Doppler ultrasound — cardiologists measure blood flow velocity in arteries and veins, detecting blockages and valve defects non-invasively.
Q5 (5 marks — 50 words): What is ITER? What are the advantages of nuclear fusion over fission?
Model Answer:
ITER (International Thermonuclear Experimental Reactor) is the world's largest fusion experiment, under construction in Cadarache, France, with 35 nations including India. Target: Q = 10 (10× energy output vs input); first plasma expected 2025. Fusion advantages over fission: (1) Nearly unlimited fuel — deuterium from seawater; (2) no long-lived radioactive waste (only short-lived activated components); (3) no risk of runaway chain reaction; (4) no greenhouse gas emissions. USA's NIF achieved fusion ignition (Q > 1) in December 2022 — historic breakthrough.
Q6 (5 marks — 50 words): Explain the three laws of Newton's motion with one practical application each.
Model Answer:
First Law (Inertia): Body at rest/uniform motion continues unless external force acts. Application: Seatbelts — in sudden braking, body continues forward (inertia); seatbelt provides the external stopping force. Second Law (F = ma): Net force = mass × acceleration. Application: Braking distance — heavier vehicle needs greater braking force to decelerate at same rate; explains why trucks have larger brakes. Third Law (Action-Reaction): Application: Rocket propulsion — exhaust gases expelled backward (action) → rocket moves forward (reaction) — works in vacuum of space.