Q&A Bank

Questions & Answers

388 answers across all subjects

Subject:Mathematics Science English Social Studies Hindi Physics Chemistry Biology Computer Science

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ScienceClass 7CBSE

A spaceship travels 36,000 km in one hour. Express its speed in km/s.

Soln: 36000 km/h= 36000/60*60 = 10 km/s

ScienceClass 7CBSE

The average age of children in Class VII is 12 years and 3 months. Express this age in seconds.

Soln: 12 years 3 months = 12 × 365 + 3 × 30 = 4470 days = 4470 × 24 × 60 × 60 s = 386208000 s

ScienceClass 7CBSE

If Boojho covers a certain distance in one hour and Paheli covers the same distance in two hours, who travels at a higher speed?

Soln: Boojho travels at a higher speed; hence he reaches the distance early.

ScienceClass 7CBSE

Paheli and Boojho have to cover different distances to reach their school, but they take the same time to reach the school. What can you say about their speed?

Soln: Because their speed will be different from one another.

ScienceClass 7CBSE

The correct symbol to represent the speed of an object is (a) 5 m/s (b) 5 mp (c) 5 m/s-1 (d) 5 s/m

Soln: Answer is (a) 5 m/s Explanation: Unit of speed is meter/ second hence the answer is (a) 5 m/s.

ScienceClass 7CBSE

If we denote speed by S, the distance by D and time by T, the relationship between these quantities is (a) S = D × T (b) T = S/D (c) S = 1/ T x D (c) S = T/D

Soln: Answer is (c) S = 1/TxD Explanation: Option c) is the correction equation because Speed = Distance/Time

ScienceClass 7CBSE

A bus travels 54 km in 90 minutes. The speed of the bus is (a) 0.6 m/s (b) 10 m/s (c) 5.4 m/s (d) 3.6 m/s

Soln: Answer is (b) 10 m/s Explanation: Speed = Distance / Time Distance = 54km = 54 x1000 = 54000m Time = 90 minutes = 90×60= 5400s Speed = 54000/5400 = 10 m/s

ScienceClass 7CBSE

Which of the following cannot be used for the measurement of time? (a) A leaking tap. (b) Simple pendulum. (c) Shadow of an object during the day. (d) Blinking of eyes.

Soln: The answer is (d) Blinking of eyes. Explanation: Blinking of the eye is not a periodic phenomenon. Eyes do not blink at a fixed interval of time. Hence Blinking of eyes cannot be used for measurement of time.

ScienceClass 7CBSE

You are given three mirrors of different types. How will you identify each one of them?

Soln: We can identify the mirrors by forming images of an object which are given as below: i) Plane mirror, in the case of a plane mirror, the image will be virtual, erect and of the same size as that of an object. ii) Concave mirror, in the case of a concave mirror, an image may be real or virtual, inverted or erect and magnified or diminished depending upon the position of the object. iii) Convex mirror, in the case of a convex mirror, an image formed will always be virtual, erect and diminished in spite of the position of the object.

ScienceClass 7CBSE

It was observed that when the distance between an object and a lens decreases, the size of the image increases. What is the nature of this lens? If you keep on decreasing the distance between the object and the lens, will you still able to obtain the image on the screen? Explain.

Soln: It is a convex lens. No, when the object is placed close to a convex lens then the image formed is virtual, which cannot be obtained on the screen.

ScienceClass 7CBSE

Suppose we wish to obtain the real image of a distant tree. Explain two possible ways in which we can do it.

Soln: Two possible ways in which the real image of a distant tree can be obtained are given below : By using a concave mirror and a screen- By using a concave mirror, a real image is formed if the distance between the mirror and the object is beyond the focus. By using a convex lens and a screen- In a convex lens, when the object is far away from the lens, the image is very close to the lens forming a real and inverted image.

ScienceClass 7CBSE

The distance between an object and a convex lens is changing. It is noticed that the size of the image formed on a screen is decreasing. Is the object moving in a direction towards the lens or away from it?

Soln: An object is moving away from the lens.

ScienceClass 7CBSE

A shopkeeper wanted to fix a mirror which would give a maximum view of his shop. What type of mirror should he use? Give reason.

Soln: The shopkeeper fixes convex mirror because forms images of object spread from large areas.

ScienceClass 7CBSE

Two different types of lenses are placed on a sheet of newspaper. How will you identify them without touching them?

Soln: The lens is a convex lens if the letters appear magnified and the lens is concave if the image appears shortened.

ScienceClass 7CBSE

An erect and enlarged image of an object is formed on a screen. Explain how this could be possible.

Soln: An erect and enlarged image of an object is formed on a screen if the object is placed upside down between F and 2F of the lens.

ScienceClass 7CBSE

The side mirror of a scooter got broken. The mechanic replaced it with a plane mirror. Mention any inconvenience that the driver of the scooter will face while using it?

Soln: A driver cannot see the traffic spread over the large area behind him.

ScienceClass 7CBSE

The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch?

Soln: If the concave reflecting surface of a torch got rusted, a beam of light will be diffused with lower intensity.

ScienceClass 7CBSE

Boojho made light from a laser torch to fall on a prism. Will he be able to observe a band of seven colours? Explain with a reason.

Soln: No, Boojho cannot observe a band of colours because laser light gives torch of only one colour.

ScienceClass 7CBSE

What type of mirror is used as a side mirror in a scooter? Why is this type of mirror chosen?

Soln: Convex mirrors are used as a side mirror in a scooter because in Convex mirrors image formed is spread over a large area. This will help the drivers to see the large area behind in the traffic.

ScienceClass 7CBSE

State whether the following statements are True or False. (a) A concave lens can be used to produce an enlarged and erect image. (b) A convex lens always produces a real image. (c) The sides of an object and its image formed by a concave mirror are always interchanged. (d) An object can be seen only if it emits light.

Soln: False- A concave lens can be used to produce a diminished and erect image. False- A convex lens always produces a virtual image True False- An object can be seen if it reflects light falling on it.

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