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What precautions would you take if lightning occurs while you are outside the house?

Answer: Lightning can be explained in terms of charges produced due to rubbing. During a thunderstorm, the air currents move upwards and the... View Article

When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

Answer: Physical change - A substance is said to undergo a physical change when only the physical properties such as the shape, size, colour,... View Article

When a glass rod is rubbed with a piece of silk cloth the rod (a) and the cloth both acquire positive charge. (b) becomes positively charged while the cloth has a negative charge. (c) and the cloth both acquire negative charge. (d) becomes negatively charged while the cloth has a positive charge.

Answer: (b) becomes positively charged while the cloth has a negative charge. When the glass rod is rubbed with silk clothes, glass quickly loses... View Article

When an electric current is passed through a conducting solution, there is a change of colour of the solution. This indicates (a) the chemical effect of current. (b) the heating effect of current. (c) the magnetic effect of current. (d) the lightning effect of current.

Answer: (a) the chemical effect of current. Electrical conductors are materials that allow electricity to flow through them easily. If we compare... View Article

When are the maximum and minimum temperatures likely to occur during the day?

Answer: Cloudy, sunny, rainy, stormy, or clear weather all are possibilities. It is a natural occurrence that keeps the atmosphere in a state of... View Article

When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

Answer: When baking soda and lemon juice are mixed, carbon dioxide gas is produced, resulting in bubbles. This is a chemical change. The reaction... View Article

When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.

Answer: When carbon dioxide is passed through lime water, it turns milky due to the formation of Calcium carbonate. When carbon dioxide is... View Article

When the cutting edge of a knife is put against a fast rotating stone to sharpen it, sparks are seen to fly. Explain the reason.

Answer: Frictional force refers to the force generated by two surfaces that contact and slide against each other. Friction is caused due to the... View Article

When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Answer: The deflection of the compass needle indicates that current is flowing through the wire. When the free ends of the tester are immersed in... View Article

When we hear a sound, does any part of our body vibrate? Name the part.

Answer: When we hear a sound our eardrum vibrates. Sound enters through the outer part of the ear, travels down a canal, and finally strikes a... View Article

Whenever the surfaces in contact tend to move or move with respect to each other, the force of friction comes into play (a) only if the objects are solid. (b) only if one of the two objects is liquid. (c) only if one of the two objects is gaseous. (d) irrespective of whether the objects are solid, liquid or gaseous.

Answer: (d) irrespective of whether the objects are solid, liquid or gaseous. Friction is the force that resists motion when the surface of one... View Article

Where do we apply a force while walking?

Answer: While walking, we apply a force on the ground, which causes the ground to apply a reaction force on our foot, allowing us to move... View Article

Which of the following can be beaten into thin sheets? (a) Zinc (b) Phosphorus (c) Sulphur (d) Oxygen

Answer: (a) Zinc Metals are minerals or substances that form naturally below the surface of the Earth. Most metals are lustrous or shiny. Metals... View Article

Which of the following cannot be charged easily by friction? (a) A plastic scale (b) A copper rod (c) An inflated balloon (d) A woollen cloth.

Answer: (b) A copper rod Friction is defined as the resistance offered by the surfaces that are in contact with each other when they move over... View Article

Which of the following contains maximum number of molecules? (a) 1g CO₂ (b) 1g N₂ (c) 1g H^{2 (d) 1g CH₄}

Answer: (c) 1g H2 NA = 6.023×1023 ⇒ (1/44) x 6.022 x 1023 = 1.368 x 1022 molecules ⇒ (1/28) x 6.022 x 1023 = 2.15 x 1022... View Article

Which of the following correctly represents 360 g of water? (i) 2 moles of H₂0 (ii) 20 moles of water (iii) 6.022 × 10²³ molecules of water (iv) 1.2044×10²⁵ molecules of water Choose the option : (a) (i) (b) (i) and (iv) (c) (ii) and (iii) (d) (ii) and (iv)

Answer: (d) (ii) and (iv) One mole of a substance is equal to the substance’s 6.022 x 1023 units. The 6.022 x 1023 number is known as the... View Article

Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer. (i) 3√t + t√2 (ii) y + 2/y (iii) x¹⁰ + y³+t⁵⁰

Answer: A polynomial is defined as an expression that is composed of variables, constants and exponents, that are combined using mathematical... View Article

Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer. (i) 4x²–3x+7 (ii) y²+√2

Answer: A polynomial is defined as an expression that is composed of variables, constants and exponents, that are combined using mathematical... View Article

Which of the following figures depicts the position of pole star correctly?

Answer: (a) The polar star is the biggest of all-stars and will be the first star to rise after sunset in the sky. It rises in the north and is... View Article

Which of the following has maximum number of atoms? (a) 18g of H₂O (b) 18g of O₂ (c) 18g of CO₂ (d) 18g of CH₄

Answer: (d) 18g of CH4 Number of atoms = Mass of substance × Number of atoms in the molecule/ Molar mass × NA NA = 6.023×1023 ⇒ 18 x 3/18 ×... View Article

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