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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

Carry out the following division: -36y³ ÷ 9y²

Answer: -4y The four important terms used in the division operation are dividend, divisor, quotient and remainder. The formula to calculate the... View Article

Carry out the following division: 12a⁸b⁸ ÷ (-6a⁶b⁴)

Answer: -2a2b4 The four important terms used in the division operation are dividend, divisor, quotient and remainder. The formula to calculate... View Article

Carry out the following division: 28x⁴ ÷ 56x

Answer: 1/2 x3 The four important terms used in the division operation are dividend, divisor, quotient and remainder. The formula to calculate... View Article

Carry out the following division: 34x³y³z³ ÷ 51xy²z³

Answer: 2/3 x2y The four important terms used in the division operation are dividend, divisor, quotient and remainder. The formula to calculate... View Article

Carry out the following division: 66pq²r³ ÷ 11qr²

Answer: 6pqr The four important terms used in the division operation are dividend, divisor, quotient and remainder. The formula to calculate the... View Article

Carry out the multiplication of the expressions in each of the following pairs. (i) 4p, q + r (ii) ab, a – b (iii) a + b, 7a²b² (iv) a² – 9, 4a (v) pq + qr + rp, 0

Answer: 4p × (q + r) ⇒ 4p × q + 4p × r ⇒ 4pq + 4pr ab × (a - b) ⇒ (ab × a) - (ab × b)... View Article

Cartilage is present in the joints of our body, which helps in their smooth movement. With advancing age, this cartilage wears off. How would this affect the movement of joints?

Answer: Cartilage is found in our body's joints and helps to minimise friction during joint movement. However, as this cartilage wears away, the... View Article

Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’. Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Answer: Recycling waste product is very important as it helps in processing waste or used products into useful or new products. Recycling also... View Article

Changes in which new substances are formed are called _________ changes.

Answer: Changes in which new substances are formed are called chemical changes. A substance is said to undergo a chemical change when the... View Article

Changes in which only _________ properties of a substance change are called physical changes.

Answer: Changes in which only physical properties of a substance change are called physical changes. A substance is said to undergo a physical... View Article

Check whether 7 + 3x is a factor of 3x³ + 7x.

Answer: A polynomial is an algebraic expression in which the exponent on any variable is a whole number. Polynomial’s degree is the highest... View Article

Choose the correct option and justify your choice : 1 tan²45°/1+tan²45° = ? (A) tan 90° (B) 1 (C) sin 45° (D) 0

Answer: (D) 0 Trigonometry values for angles 0°, 30°, 45°, 60°and 90°, with respect to sin, cos, tan, cot, sec, cosec... View Article

Choose the correct option and justify your choice : 2tan 30°/1+tan²30° = ? (A) sin 60° (B) cos 60° (C) tan 60° (D) sin 30°

Answer: (A) sin 60° Trigonometry values for angles 0°, 30°, 45°, 60°and 90°, with respect to sin, cos, tan, cot, sec,... View Article

Choose the correct option and justify your choice : sin 2A = 2 sin A is true when A = ? (A) 0° (B) 30° (C) 45° (D) 60°

Answer: (A) 0° sin 2A = 2 sin A is true when A = 0° To find the value of A, substitute the degree given in the options one by one As sin... View Article

Choose the correct option and justify your choice: 2tan30°/1-tan²30° = ? (A) cos 60° (B) sin 60° (C) tan 60° (D) sin 30°

Answer: (C) tan 60° Substitute the of tan 30° in the given equation 2 tan30°/1-tan230° Trigonometry values for angles... View Article

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