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Obtain the product of (i) xy, yz, zx (ii) a, -a² , a³

Answer: xy × yz × zx ⇒ (x × x) × (y × y) × (z × z) ⇒ x2 × y2 × z2 ⇒ x2... View Article

Obtain the volume of rectangular boxes with the following length, breadth and height respectively. (i) 5a, 3a², 7a⁴ (ii) 2p, 4q, 8r (iii) xy, 2x²y, 2xy² (iv) a, 2b, 3c

Answer: A Rectangle is a four sided-polygon, having all the internal angles equal to 90 degrees. The two sides at each corner or vertex, meet at... View Article

One day Reeta went to a jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?

Answer: The gold jewellery must be dipped in a liquid called aqua regia, that is a mixture of hydrochloric and nitric acid, to polish it. When... View Article

One of the most common applications of chemical effect of electric current is ______________.

Answer: One of the most common applications of the chemical effect of electric current is electroplating. Electroplating is the process of... View Article

Outline your role as an active citizen in relation to sanitation.

Answer: Sanitation refers to public health conditions such as drinking clean water, sewage treatment, etc. All the effective tools and actions... View Article

Paheli and Boojho observe a bright object in the night sky which was not twinkling. Paheli says, it is a star and Boojho says it is a planet. Who is correct?

Answer: Boojho is right because only planets cannot twinkle whereas stars emit light from a far distance and they twinkle. Our sun is the... View Article

Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise she found that the compass needle showed deflection. What could be the reasons?

Answer: Rainwater is considered to be pure water, but when it falls to the earth, it dissolves various acidic gases such as carbon dioxide,... View Article

Paheli saw the moon through a glass window at 8:00 p.m. She marked the position of the moon on the glass pane. She got up at 4 a.m. in the morning. Will the moon be visible at the same position?

Answer: No, Because the position of the moon keeps changing during the night. The moon does not produce its own light, whereas the Sun and other... View Article

Paheli set up an experiment using liquid A in the beaker as shown in Fig. She observed that the bulb glows. Then she replaced the liquid A by another liquid B. This time the bulb did not glow. Boojho suggested replacing the bulb by an LED. They observed that the LED glows. Explain.

Answer: A normal bulb cannot convert very little electrical energy or voltage to light energy, whereas an LED can. LED lights are able to... View Article

Paheli wants to deposit silver on an iron spoon. She took a silver nitrate (AgNO³) solution in a beaker and set up a simple circuit for electroplating. Which terminal of the battery should the spoon be connected to? What material should the other electrode be made of?

Answer: The spoon should be connected to the negative terminal of the battery. The other electrode should be made of silver. Electroplating is... View Article

Part of the eye which controls the light entering is called (a) iris (b) cornea (c) lens (d) retina

Answer: (a) Iris Iris a dark muscular tissue and ring-like structure behind the cornea are known as the iris. The colour of the iris actually... View Article

Pitch of sound is determined by its (a) frequency (b) amplitude (c) speed (d) loudness

Answer: (a) frequency The Pitch of the sound depends on the frequency of vibration of the waves. The sound is loud and has a high pitch if the... View Article

Plastic straws A and B are rubbed with a dry cotton cloth. What will happen if they are brought near each other?

Answer: They will repel each other because when the plastic straws are rubbed with the cotton cloth, they both acquire the same charge, and like... View Article

Prepare a list of objects around you that are electroplated.

Answer: Electroplating is a process that uses an electric current to reduce dissolved metal cations so that they form a thin coherent metal... View Article

Prove the following identities, where the angles involved are acute angles for which the expressions are defined. (i) (1 + sec A)/sec A = sin²A/(1-cos A) [Hint: Simplify LHS and RHS separately] (ii) (cos A–sin A+1)/( cos A +sin A–1) = cosec A + cot A, using the identity cosec²A = 1+cot²A.

Answer: (i) (1 + sec A)/sec A = sin2A/(1-cos A) First find the simplified form of L.H.S L.H.S. = (1 + sec A)/sec A Since secant function is... View Article

Prove the following identities, where the angles involved are acute angles for which the expressions are defined. (i) (cosec θ – cot θ)2 = (1-cos θ)/(1+cos θ) (ii) cos A/(1+sin A) + (1+sin A)/cos A = 2 sec A (iii) tan θ/(1-cot θ) + cot θ/(1-tan θ) = 1 + sec θ cosec θ [Hint : Write the expression in terms of sin θ and cos θ]

Answer: To prove this, first take the Left-Hand side (L.H.S) of the given equation, to prove the Right Hand Side (R.H.S) L.H.S. = (cosec... View Article

Prove the following identities, where the angles involved are acute angles for which the expressions are defined. (i) (sin θ – 2sin3θ)/(2cos3θ-cos θ) = tan θ (ii) (sin A + cosec A)² + (cos A + sec A)² = 7 + tan²A + cot²A (iii) (cosec A – sin A)(sec A – cos A) = 1/(tan A+cotA) [Hint : Simplify LHS and RHS separately]

Answer: L.H.S. = (sin θ – 2sin3θ)/(2cos3θ – cos θ) Take sin θ as in numerator and cos θ in... View Article

Prove the following identities, where the angles involved are acute angles for which the expressions are defined. (i) √(1+sin A)/(1-sin A) = sec A + tan A (ii) (1+tan²A/1+cot²A) = (1-tan A/1-cot A)² = tan²A

Answer: sec2A + tan2A = 1 ⇒ sec A + tan A = R.H.S L.H.S. = (1+tan2A/1+cot2A) Since cot function is the inverse of tan function, = (1 +... View Article

Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

Answer: For the summer, Rana should buy a cotton shirt rather than a synthetic shirt. Cotton is a good water absorbent. So that it can absorb and... View Article

Represent -2/11, -5/11, -9/11 on a number line.

Answer: A number line is a pictorial representation of numbers on a straight line. It’s a reference for comparing and ordering numbers. It can... View Article

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