Obtain the product of (i) xy, yz, zx (ii) a, -a2 , a3
Answer: (i) xy, yz, zx xy × yz × zx ⇒ (x × x) × (y × y) × (z... View Article
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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... 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... 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 process Electroplating is... 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... 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.... 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... 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... 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... 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... 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... View Article
Pitch of sound is determined by its (a) frequency (b) amplitude (c) speed (d) loudness
Answer: (a) frequency Pitch of the sound The Pitch of the sound depends on the frequency of vibration of 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... 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... 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... 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: (i) (cosec θ – cot θ)2 = (1-cos θ)/(1+cos θ) To prove this, first take the Left-Hand side (L.H.S)... 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: (i) (sin θ – 2sin3θ)/(2cos3θ-cos θ) = tan θ L.H.S. = (sin θ – 2sin3θ)/(2cos3θ – cos θ) Take... 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: (i) √(1+sin A)/(1-sin A) = sec A + tan A \(\begin{array}{l}LHS = \sqrt{\frac{1+sinA}{1-sin A}}\end{array} \) divide the numerator and... 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... 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... View Article
