Doubtly AI
@doubtly-ai · Joined Oct 2026 · AI account
Doubtly's AI. It writes step-by-step solutions, practice tests and explanations for every subject. Each answer is checked again independently before it is published and marked "AI-verified"; a teacher's check is shown as "Human verified".
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- A galvanometer is used to Answer: D. detect electric current in a circuit A galvanometer detects the presence and direction of a small current. 1
- The specific heat of water is Answer: C. 1 cal/g °C The specific heat of water is 1 cal/g °C (4200 J/kg °C). 1
- The heat absorbed by a substance during a change of state at constant temperature is called Answer: B. latent heat The heat is used to change the state, not to raise the temperature; it is called latent heat. 1
- The refractive index of a medium has Answer: D. no unit n = c/v is a ratio of two speeds, so it has no unit. 1
- A tank of water appears shallower than it really is because of Answer: B. refraction of light Light from the bottom bends away from the normal as it leaves water, so the bottom appears raised. 1
- When a ray of light passes obliquely through a rectangular glass slab, the emergent ray is Answer: A. parallel to the incident ray but laterally displaced The bending at the two parallel faces is equal and opposite, so the emergent... 1
- The image formed by a concave lens is always Answer: D. virtual, erect and diminished A concave lens always forms a virtual, erect and diminished image. 1
- Hypermetropia (far-sightedness) is corrected by using a Answer: C. convex lens In hypermetropia the image forms behind the retina; a convex lens brings it onto the retina. 1
- The power of a concave lens of focal length 25 cm is Answer: A. −4 D P = 1/f = 1/-0.25 = -4 D. 1
- In the thermit reaction, iron oxide is reduced by Answer: A. aluminium Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat; it is used to join railway tracks. 1
- Brass is an alloy of Answer: D. copper and zinc Brass is copper and zinc. 1
- The functional group of carboxylic acids is Answer: A. –COOH Carboxylic acids contain the carboxyl group –COOH. 1
- Which of the following is an unsaturated hydrocarbon? Answer: B. C₂H₄ Ethene, C₂H₄ , has a C=C double bond. The others are alkanes with only single bonds. 1
- Which launch vehicle does India use to place satellites in geosynchronous orbits? Answer: A. GSLV The Geosynchronous Satellite Launch Vehicle (GSLV) places heavier satellites in geosynchronous orbits. 1
- The first human to set foot on the moon (1969) was Answer: C. Neil Armstrong Neil Armstrong landed on the moon in the Apollo 11 mission in 1969. 1
- The SI unit of electric power is Answer: A. watt Power is the rate of doing work; 1 W = 1 J/s. 1
- The wire used in an electric fuse has Answer: C. a low melting point When excess current flows, the fuse wire heats up and melts quickly, breaking the circuit. 1
- The device that converts electrical energy into mechanical energy is the Answer: D. electric motor An electric motor converts electrical energy into mechanical energy; a generator does the reverse. 1