Learn and Grow

 E X E R C I S E S   CHAPTER  13  Our Environment 1. Which of the following groups contain only biodegradable items? (a) Grass, flowers, and leather (b) Grass, wood, and plastic (c) Fruit-peels, cake, and lime-juice (d) Cake, wood, and grass Answer: (d) Cake, wood, and grass Explanation: Biodegradable items are those that can be broken down naturally by microorganisms. Cake, wood, and grass are organic materials that will decompose over time. Leather is biodegradable, but plastic is not, so option (b) is incorrect. Fruit peels, cake, and lime-juice are also biodegradable, but option (d) fits better as all items listed are biodegradable. 2. Which of the following constitute a food-chain? (a) Grass, wheat, and mango (b) Grass, goat, and human (c) Goat, cow, and elephant (d) Grass, fish, and goat Answer: (b) Grass, goat, and human Explanation: A food chain is a sequence in which organisms transfer energy by eating and being eaten. ...

  E X E R C I S E S   CHAPTER  12  Magnetic Effects of  Electric Current  1. Which of the following correctly describes the magnetic field near a long straight wire? (a) The field consists of straight lines perpendicular to the wire. (b) The field consists of straight lines parallel to the wire. (c) The field consists of radial lines originating from the wire. (d) The field consists of concentric circles centered on the wire. Answer: (d) The field consists of concentric circles centered on the wire. Explanation: The magnetic field around a long straight current-carrying wire forms concentric circles centered on the wire. The direction of the field is given by the right-hand thumb rule. 2. At the time of short circuit, the current in the circuit: (a) reduces substantially. (b) does not change. (c) increases heavily. (d) varies continuously. Answer: (c) increases heavily. Explanation: In the case of a short circuit, the resi...

  E X E R C I S E S CHAPTER  11  Electricity   1. A piece of wire of resistance R R  is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R ′ R' , then the ratio R / R ′ R/R'  is: (a) 1/25 (b) 1/5 (c) 5 (d) 25 Answer: If the wire is cut into 5 equal parts, the resistance of each part will be R 5 \frac{R}{5} ​ . When connected in parallel, the equivalent resistance R ′ R'  is given by the formula: 1 R ′ = 1 R 1 + 1 R 2 + ⋯ \frac{1}{R'} = \frac{1}{R_1} + \frac{1}{R_2} + \cdots Since all parts are identical, this simplifies to: 1 R ′ = 5 × 1 R / 5 = 5 R / 5 = 25 R \frac{1}{R'} = 5 \times \frac{1}{R/5} = \frac{5}{R/5} = \frac{25}{R} ​ Thus, R ′ = R 25 R' = \frac{R}{25} , and the ratio R / R ′ = 25 R/R' = 25 . Correct answer: (d) 25 2. Which of the following terms does not represent electrical power in a circuit? (a) I 2 R I^2R (b) I R 2 IR^2 (c) V I VI (d) V 2 R \fra...

  E X E R C I S E S   CHAPTER  10  The Human Eye and  the Colourful World 1. The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due to: Answer: (d) accommodation. Explanation: Accommodation refers to the ability of the eye to change the shape of the lens to focus on objects at different distances. 2. The human eye forms the image of an object at its: Answer: (d) retina. Explanation: The retina is the light-sensitive layer at the back of the eye where the image is formed and transmitted to the brain. 3. The least distance of distinct vision for a young adult with normal vision is about: Answer: (c) 25 cm. Explanation: The least distance of distinct vision (near point) for a normal human eye is typically about 25 cm. 4. The change in focal length of an eye lens is caused by the action of the: Answer: (c) ciliary muscles. Explanation: The ciliary muscles control the shape of...