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Add the following: a – b + ab, b – c + bc, c – a + ac

Answer: ab + bc + ca (a - b + ab) + (b - c + bc) + (c - a + ac) = a - b + ab + b - c + bc + c - a + ac (a - b + ab) + (b - c + bc) + (c - a +... View Article

Add the following: ab – bc, bc – ca, ca – ab

Answer: 0 (ab - bc) + (bc - ca) + (ca - ab) = ab - bc + bc - ca + ca - ab (ab - bc) + (bc - ca) + (ca - ab) = ab - ab - bc + bc - ca + ca (ab -... View Article

Add the following: l² + m², m² + n², n² + l², 2lm + 2mn + 2nl

Answer: 2l2 + 2m2 + 2n2 + 2lm + 2mn + 2nl (l2 + m2) + (m2 + n2) + (n2 + l2) + (2lm + 2mn + 2nl) (l2 + m2) + (m2 + n2) + (n2 + l2) + (2lm +... View Article

Add: 2x (z – x – y) and 2y (z – y – x)

Answer: 2xz - 4xy + 2yz - 2x2 - 2y2 2x (z - x - y) + 2y (z - y - x) 2x (z - x - y) + 2y (z - y - x) = (2x × z) - (2x × x) - (2x... View Article

Add: p ( p – q), q ( q – r) and r ( r – p)

Answer: p2 + q2 + r2 - pq - qr - pr p( p - q) + q(q - r) + r( r - p) = (p2 - pq) + (q2 - qr) + (r2 - pr) = p2 - pq + q2 - qr + r2 - pr = p2 +... View Article

Air moves from a region of _ pressure to a region of_ pressure.

Answer: Air moves from a region of high air pressure to a region of low air pressure. Air always flows from high-pressure areas to low-pressure... View Article

All the stars are at the same distance from us. (True or False)

Answer: All the stars are at the same distance from us - False Stars are celestial bodies that emit their own light and heat. Our sun is an... View Article

Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

Answer: Ammonia is basic in nature. The chemical formula for ammonia is NH3. It is a colourless gas. It is made up of two elements: hydrogen... View Article

An alarm bell is kept inside a vessel as shown in Fig. A person standing close to it can distinctly hear the sound of the alarm. Now if the air inside the vessel is removed completely how will the loudness of alarm get affected for the same person?

Answer: Air needs a medium to get transmitted. If we slowly remove the air inside the bottle. Sound will not be having medium to travel as it... View Article

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

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