Do stars emit light only during night?
Question: Do stars emit light only during night? Solution: No, stars emit light all the time. But, we are not able to see their light due to excess brightness of the Sun....
Read More →The change in seasons on the earth occurs because
Question: The change in seasons on the earth occurs because (a) the distance between the earth and the sun is not constant (b) the axis of rotation of the earth is parallel to the plane of its orbit (c) the axis of rotation of the earth is perpendicular to the plane of its orbit (d) the axis of rotation of the earth is tilted with respect to the plane of its orbit Solution: (d) The axis of rotation of the earth is not perpendicular to the plane of its orbit. The tilt is responsible for the chang...
Read More →Suppose a new planet is discovered
Question: Suppose a new planet is discovered between Uranus and Neptune. Its time period would be (a) less than that of Neptune (b) more than that pf Neptune (c) equal to that of Neptune or Uranus (d) less than that of Uranus Solution: (a) As we know that, the,time period is directly proportional to the distance from the sun, so the new planet discovered between Uranus and Neptune will have less time period than the neptune and greater than the Uranus....
Read More →An astronaut standing on the surface
Question: An astronaut standing on the surface of the moon throws a ball upwards. The ball would (a) directly fall down from the point it is released (b) hang in space (c) go up and then, come back to the surface of the moon (d) keep going up never to come back Solution: (c) The ball will go up and then comes down because at moon, acceleration due to gravity is less than that of the earth....
Read More →The sun appears to move from
Question: The sun appears to move from east to west around the earth. This means that earth rotates from (a) East to West (b) West to East (c) North to South (d) West to North Solution: (b) The sun appears to move from East to West around the earth, it means that the earth rotates in opposite direction, i.e. from West to East....
Read More →Solve this
Question: If $\sin \theta=\frac{-1}{2}$ and $\theta$ lies in Quadrant IV, find the values of all the other five trigonometric functions. Solution: Given: $\sin \theta=\frac{-1}{2}$ Since, $\theta$ is in IVth Quadrant. So, sin and tan will be negative but cos will be positive. We know that, $\sin ^{2} \theta+\cos ^{2} \theta=1$ Putting the values, we get $\left(-\frac{1}{2}\right)^{2}+\cos ^{2} \theta=1$ [given] $\Rightarrow \frac{1}{4}+\cos ^{2} \theta=1$ $\Rightarrow \cos ^{2} \theta=1-\frac{1}...
Read More →Morning star is the name given to
Question: Morning star is the name given to (a) Pole star (b) star Sirius (c) planet Jupiter (d) planet Venus Solution: (d) Morning star is the name given to the planet Venus because sometimes it appears in the eastern sky before sunrise....
Read More →How is the phenomenon
Question: How is the phenomenon of reflection used in making a kaleidoscope. What are the applications of a kaleidoscope? Solution: Kaleidoscope is a cylinder with three mirrors containing loose, coloured objects such as beads or pebbles and bits of glass. As the viewer looks into one end, light entering the other end, creates a colourful pattern due to reflection. It works on the principle of multiple reflection, where several mirrors are placed at an angle (usually 60) to one another. Typicall...
Read More →Explain the process
Question: Explain the process which enables us to perceive motion in a cartoon film. Solution: In a cartoon film, we see the projection of static pictures on the screen in a specific order. Generally, the static pictures are made to move across the eye in a sequence at the rate of 24 pictures per second (faster than 16 per second) giving us the perception of a moving picture....
Read More →Which part of the eye gets
Question: Which part of the eye gets affected if someone is suffering from cataract? How is it treated? Solution: In people (particularly old aged) suffering from cataract, the eye lens becomes clouded. Cataract is treated by replacing the opaque lens with a new artificial lens....
Read More →What kind of lens is there
Question: What kind of lens is there in our eyes? Where does it form the image of an object? Solution: Convex lens is present in our eyes, which focuses light on the back of the eye, on a layer called retina. So, it forms the image of an object at retina....
Read More →Eyes of the nocturnal birds have large
Question: Eyes of the nocturnal birds have large cornea and a large pupil. How does this structure help them? Solution: The size of the eyes of nocturnal bird is large. Eyes of the nocturnal birds having large cornea with a wider pupil, can collect more ambient light which help them to see the objects even at night....
Read More →What happens to light
Question: What happens to light when it gets dispersed? Give an example. Solution: Light is splitted into its constituent colours, when it gets dispersed, e.g. Rainbow formation is due to the dispersion of white light after passing through water droplets....
Read More →Solve this
Question: If $\cos \theta=\frac{-\sqrt{3}}{2}$ and $\theta$ lies in Quadrant III, find the value of all the other five trigonometric functions. Solution: Given: $\cos \theta=\frac{-\sqrt{3}}{2}$ Since, is in IIIrd Quadrant. So, sin and cos will be negative but tan will be positive We know that, $\cos ^{2} \theta+\sin ^{2} \theta=1$ Putting the values, we get $\left(-\frac{\sqrt{3}}{2}\right)^{2}+\sin ^{2} \theta=1$ [given] $\Rightarrow \frac{3}{4}+\sin ^{2} \theta=1$ $\Rightarrow \sin ^{2} \thet...
Read More →Boojho while waving his hand
Question: 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? Solution: The impression of an image persists for about 1/16th of a second on the retina. This is known as persistence of vision. If still images of a moving object are flashed on the eye at a rate faster than 16 per second, then the eye perceives this object as moving. So, in case by waving hand very fast in front of eyes, the rate of movement of hand...
Read More →Name the part of the eye
Question: Name the part of the eye which gives colour to the eyes. Solution: Iris is the part of the eye which gives its distinctive colour. e.g. If a person is said to have blue eyes, then that actually refers to the blue colour of the iris....
Read More →Which of the following statements
Question: Which of the following statements is correct regarding rods and cones in the human eye? (a) Cones are sensitive to dim light. (b) Cones are sensitive to bright light (c) Rods are sensitive to bright light (d) Rods can sense colour Solution: (b) Cones are sensitive to bright light and they sense colour. However, rods are sensitive dim light....
Read More →We can see a non-luminous object when the light
Question: We can see a non-luminous object when the light (a) emitted by the object falls on the eye (b) is reflected from the object towards our eye (c) completely passes through the object (d) gets completely absorbed by the object Solution: (b) We can see a non-luminous object (object that does not produce its own light), when light reflected by the object enters our eyes....
Read More →Part of the eye which controls
Question: Part of the eye which controlsthe entering of light is called (a) iris (b) cornea (c) lens (d) retina Solution: (a) Iris is a dark muscular structure behind the cornea, which controls the amount of light entering into the eye....
Read More →If the metal clip used in the electroscope
Question: If the metal clip used in the electroscope is replaced by an ebonite rod and a charged body is brought in contact with it, will there be any effect on the aluminium strips? Explain. Solution: No, there will not be any repulsion between the aluminium strips. The charged body will not transfer any type of charge to the ebonite rod as ebonite rod is an insulator. Therefore, there will be no charge on the aluminium strips and no repulsion of the strips will occur....
Read More →What precautions would you take
Question: What precautions would you take if lightning occurs while you are outside the house? Solution: Precautions to be taken, while we are outside the house during tightning (i) Do not stand underneath a natural lightning rod such as pole or a tall tree. (ii)Stand away from any fountain or any other water body. (iii)Stay away from tractors or other metal equipments like wire fences, metal pipes, rails, etc....
Read More →Explain why it is safer to use a wireless
Question: Explain why it is safer to use a wireless telephone instead of a landline telephone during lightning. Solution: During lightning, an electric charge may discharge through telephone cords of landline telephone and may become dangerous. Therefore, it is safer to use mobile phones and wireless/cordless phones during lightning....
Read More →Mention three precautions tliat you
Question: Mention three precautions tliat you will take to protect yourself if earthquake strikes when you are inside the house. Solution: Three precautions that we should take if we are inside the house.during an earthquake (i) We should get under a table or a desk and stay there till the shaking stops. (ii)We should pick a safe place where tall and heavy things may not fall on us. (iii)If we are in bed, then we should not get up and protect our head with a pillow....
Read More →Explain how lightning takes place.
Question: Explain how lightning takes place. Solution: During the development of a thunderstorm, the air currents move in upward direction while the water droplets move in downward direction. These movements cause separation of charges. The positive charges collect near the upper edges of the clouds and negative charges collect near the lower edges of the clouds. Accumulation of positive charges near the ground also takes place. When the magnitude of collected charges become large, the air canno...
Read More →The strips of an electroscope diverge
Question: The strips of an electroscope diverge when a charged body is brought in contact with the metal clip. Now the clip is touched gently by our hand. What will happen to the strips? Explain. Solution: If we touch the strip standing on the ground (not on any insulating base), then the charge on the strip will pass through our hand to the ground and the strips will contract....
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