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An archer shoots an arrow in the air horizontally. However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain why the arrow ultimately falls down.

Answer: The archer shoots an arrow by stretching the bowstring with muscular force. When the string is released, it reverts to its previous... View Article

An astronaut standing on the surface of the moon throws a ball upwards. The ball would (a) directly fall down from the point it is released. (b) hang in space. (c) go up and then come back to the surface of the moon. (d) keep going up never to come back.

Answer: (c) go up and then come back to the surface of the moon. Because the acceleration due to gravity on the moon is lower than on Earth, the... View Article

An electric current can produce (a) heating effect only. (b) chemical effect only. (c) magnetic effect only. (d) chemical, heating, and magnetic effects.

Answer: (d) chemical, heating, and magnetic effects. Electric Current is the rate of flow of electrons in a conductor. The SI Unit of electric... View Article

An electric current is passed through a conducting solution. List any three possible observations.

Answer: When an electric current passes through a conducting liquid, it gets decomposed into ions. The conducting solution has free ions... View Article

An electroscope is a device which is used to find if an object is (a) charged (b) magnetic (c) free of cracks (d) hot

Answer: (a) charged An electroscope is a device that may be used to determine whether or not an object is charged. It is made up of two metallic... View Article

An object is vibrating at 50 hertz. What is its time period? (a) 0.02 s (b) 2 s (c) 0.2 s (d) 20.0 s

Answer: (a) 0.02 s We know that Frequency (f) = 1/ Time period Time period = 1/ Frequency Given parameter An object is vibrating at 50 hertz. 50... View Article

Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one. (i) Process – A is a chemical change. (ii) Process – B is a chemical change (iii) Both processes A and B are chemical changes. (iv) None of these processes is a chemical change

Answer: (iii) Both processes A and B are chemical changes Physical change - A substance is said to undergo a physical change when only the... View Article

Bathing outdoors should be avoided during a thunderstorm. (True & False)

Answer: True A thunderstorm is a storm with lightning and thunder. It’s produced by a cumulonimbus cloud, usually producing gusty winds,... View Article

Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

Answer: The above solution may be neutral or basic in nature as both of them will not change the colour of the blue litmus paper. The litmus... View Article

Boojho and Paheli performed experiments taking similar bulbs and cells but two different solutions A and B as shown in Fig. They found that the bulb in the setup A glows more brightly as compared to that of the setup B. You would conclude that (a) higher current is flowing through the circuit in setup A. (b) higher current is flowing through the circuit in setup B. (c) equal current is flowing through both the circuits. (d) the current flowing through the circuits in the two setups cannot be compared in this manner.

Answer: (a) higher current is flowing through the circuit in setup A. Because solution A is a better conductor of electricity than solution B,... View Article

Boojho made the circuit given in Fig. and observed that the bulb did not glow. On Paheli’s suggestion, he added one more cell in the circuit. The bulb now glows. Explain.

Answer: The bulb did not initially glow because one of the cells could not produce enough voltage to cause the current to glow the bulb. When a... View Article

Boojho made the circuit shown in Fig. He wanted to observe what happens when an electric current is passed through water. But he forgot to add a few drops of lemon juice to water. Will it make any difference to his observations? Explain.

Answer: If the water is distilled, it will not conduct electricity without the addition of lemon juice, and no current will flow across the... View Article

Boojho planned activity to observe an object A through pipes as shown in Fig., so that he could see objects which he could not directly see. (a) How many mirrors should he use to see the objects? (b) Indicate the positions of the mirrors in the figure. (c) What must be the angle with respect to the incident light at which he should place the mirrors? (d) Indicate the direction of the rays in the figure. (e) If any of the mirrors are removed, will he be able to see the objects?

Answer: a) Three mirrors should he use to see the objects. b) c) Mirrors should be placed at an angle of 45° with respect to the incident... View Article

Boojho saw a cracker burst at night at a distance from his house. He heard the sound of the cracker a little later after seeing the cracker burst. Give the reason for the delay in hearing the sound.

Answer: Sound travels at a significantly slower rate than light. Sound travels at a speed of around 330 metres per second in air. Light will... View Article

Boojho while waving his hand very fast in front of his eyes, observes that his fingers appear blurred. What could be the reason for it?

Answer: The impression of an image does not fade from our retina instantaneously but rather remains for 1/16th of a second. If we move our hands... View Article

Boojho’s uncle has set up an electroplating factory near his village. He should dispose of the waste of the factory (a) in the nearby river. (b) in the nearby pond. (c) in the nearby cornfield. (d) according to the disposal guidelines of the local authority.

Answer: (d) according to the disposal guidelines of the local authority. Waste is defined as unwanted and unusable materials and is regarded as... View Article

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