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Name the property under multiplication used in the following. -4/5 × 1 = 1 × (-4/5) = -4/5

Answer: The multiplicative inverse of a number N is represented by 1/N or N-1. It is also called reciprocal, derived from the Latin word... View Article

Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?

Answer: Richter scale is used to measure the destructive energy of an earthquake. The scale has a reading from 1 to 10. The Richter scale is a... View Article

Name three liquids, which when tested in the manner shown in Fig., may cause the magnetic needle to deflect.

Answer: Saltwater Lemon juice Vegetable oil Any liquid solution containing acidic or basic salt will cause this effect. A solution ionises and... View Article

Name two musical instruments which produce sound by vibrating strings?

Answer: Guitar and sitar are two musical instruments with vibrating strings that make sound. The vibrating part in a sitar are stretched... View Article

Near the earth’s surface air rises up whereas _ air comes down.

Answer: Near the earth’s surface, warm air rises up whereas cold air comes down. The movement of air is mainly caused by the differences... View Article

Observe Fig. Which of these two circuits A or B shows the correct observation?

Answer: Because a greenish blue spot is always created around the positive terminal of the battery, Circuit A indicates the correct observation.... View Article

Observe the circuit given in Fig. Boojho set up this circuit for purification of copper. What will be the nature of – (i) plate A (ii) plate B (iii) the solution? Explain the process of purification.

Answer: (i) In plate A- Pure copper (ii) In plate B- Impure copper (iii) The solution – Copper sulphate solution Electroplating is the... View Article

Observe the following circuit given in Fig. Current does not flow in the circuit if there is a gap between the two wires. Does it indicate that air is a poor conductor of electricity? Does air never conduct electricity? Explain.

Answer: Air is a poor conductor of electricity in general. However, under some conditions, such as when lightning strikes, air conducts... View Article

Observe the following circuits carefully. In which circuit will the bulb glow. Write ‘Yes’ or ‘No’ in the blank space provided along each of the circuit given in Fig.

Answer: No Yes. Because iron is a metal, it is an excellent conductor of electricity. No. Eraser is material which does not a conductor of... View Article

Observe the vessels A, B, C and D shown in Fig. carefully. The volume of water taken in each vessel is as shown. Arrange them in the order of decreasing pressure at the base of each vessel. Explain.

Answer: The pressure at depth due to the liquid column is determined by the Gravitational acceleration (g) The density of the liquid The liquid... View Article

Obtain the product of (i) 2, 4y, 8y² , 16y³ (ii) a, 2b, 3c, 6abc (iii) m, -mn, mnp

Answer: 2 × 4y × 8y2 × 16y3 ⇒ (2 × 4 × 8 × 16) × (y × y2 × y3) We know that, We... View Article

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

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