#ssc 10th
- An object is placed 15 cm from a convex lens of focal length 10 cm. The image is formed at Answer: B. 30 cm on the other side of the lens 1/v - 1/u = 1/f ⇒ 1/v = 1/10 + 1/-15 = 1/30 , so v = +30 cm (real image on the other side). 1
- An object is placed at \(2F_1\) of a convex lens. The image is formed Answer: A. at 2F₂ , real, inverted and of the same size For an object at 2F₁ , the image is at 2F₂ , real, inverted and of the same size as... 1
- Two lenses of power +3 D and −1 D are kept in contact. The combination behaves as a Answer: D. convex lens of focal length 50 cm P = 3 + (-1) = +2 D, so f = 1/2 m = 50 cm. Positive power means it acts as a convex lens. 1
- The value of the universal gravitational constant G is Answer: C. 6.67 × 10⁻¹¹ N m² kg⁻² G = 6.67 × 10⁻¹¹ N m² kg⁻². It is the same everywhere in the universe. 1
- According to Kepler's third law, the square of the period of revolution of a planet around the sun is directly proportional to Answer: C. the cube of its mean distance from the sun Kepler's third law: T² ∝ r³ . 1
- The SI unit of weight is Answer: D. newton Weight is a force ( W = mg ), so its SI unit is the newton. 1
- The mass of a person on the earth is 60 kg. His mass on the moon will be Answer: A. 60 kg Mass is the amount of matter in a body and does not change from place to place. Only weight changes. 1
- The value of g at the centre of the earth is Answer: C. zero As we go deeper into the earth, g decreases, and it becomes zero at the centre. 1
- If the distance between two masses is doubled, the gravitational force between them becomes Answer: D. one fourth F ∝ 1/d² . Doubling d makes F become 1/4 of its value. 1
- The escape velocity from the surface of the earth is about Answer: B. 11.2 km/s v_esc = √(2GM/R) ≈ 11.2 km/s for the earth. 1
- A stone is dropped from a height of 20 m. Taking \(g = 10\) m/s², the time it takes to reach the ground is Answer: A. 2 s s = 1/2gt² ⇒ 20 = 5t² ⇒ t = 2 s. 1
- The value of g at a height equal to the radius of the earth (R) above its surface is Answer: A. g/4 g ∝ 1/r² . At height R, the distance from the centre is 2R, so g becomes g/4 . 1
- The SI unit of specific heat capacity is Answer: B. J/kg °C Specific heat is the heat needed to raise the temperature of unit mass by 1 °C, so its SI unit is J/kg °C. 1
- The density of water is maximum at Answer: D. 4 °C Because of the anomalous behaviour of water, its volume is minimum and density maximum at 4 °C. 1
- The specific latent heat of fusion of ice is Answer: B. 80 cal/g 1 g of ice at 0 °C needs 80 cal to become water at 0 °C. 1
- An object falls freely from a height of 45 m. Taking \(g = 10\) m/s², its velocity on reaching the ground is Answer: A. 30 m/s v² = u² + 2gs = 0 + 2 × 10 × 45 = 900 ⇒ v = 30 m/s. 1
- The heat required to raise the temperature of 2 kg of water by 10 °C is (specific heat of water = 4200 J/kg °C) Answer: D. 84000 J Q = mcΔ T = 2 × 4200 × 10 = 84000 J. 1
- Ice melts when pressure is applied and refreezes when the pressure is removed. This process is called Answer: D. regelation This is regelation. 1
- Hope's apparatus is used to study Answer: A. the anomalous behaviour of water Hope's apparatus shows that water has its maximum density at 4 °C. 1
- When air is saturated with water vapour, its relative humidity is Answer: D. 100% Saturated air holds the maximum vapour possible at that temperature, so relative humidity is 100%. 1
- 100 g of water at 80 °C is mixed with 100 g of water at 20 °C. Assuming no heat loss, the final temperature is Answer: A. 50 °C Heat lost = heat gained: 100(80 - T) = 100(T - 20) ⇒ T = 50 °C. 1
- The heat required to melt 500 g of ice at 0 °C completely into water at 0 °C is Answer: C. 40000 cal Q = mL = 500 × 80 = 40000 cal. 1
- Decomposition of water into hydrogen and oxygen by passing electric current is called Answer: D. electrolytic decomposition 2H₂O xrightarrowelectricity 2H₂ + O₂ . Electric energy causes the decomposition. 1
- A copper vessel left in moist air gets a green coating. This coating is mainly Answer: C. copper carbonate Copper reacts with moist CO₂ in air to form a green layer of copper carbonate. This is corrosion of copper. 1