Class 7 Science Curiosity Chapter 11 MCQ – Light: Shadows and Reflections

Luminous objects emit their own light. The Sun and Pole Star are stars that produce light themselves. The Moon, planets, and an ordinary mirror do not make their own light; we see them because they reflect light.

The Moon looks bright because sunlight falls on it and is reflected towards us. It does not produce its own light. Objects that are visible by reflected light, rather than by light they emit themselves, are called non-luminous.

Fireflies produce their own light and use it to communicate. The chapter introduces them as an example of light in nature. It also mentions that light pollution, reduced forest cover, and excessive tourism can threaten their numbers.

Light from the torch can pass through all three holes when they are in one straight line. Moving a matchbox out of line blocks the path. This observation supports the idea that light travels in a straight line.

In the activity, light from the candle travels along the straight pipe to the eye. When the pipe bends, its wall blocks that straight path. The flame is therefore no longer visible through the pipe in this arrangement.

A translucent material allows light to pass through only partially. This differs from a transparent material, which lets almost all light pass, and an opaque material, which blocks it. Tracing paper is used as a translucent material in the chapter.

Opaque materials block light instead of allowing it to pass through. When an opaque object lies between a light source and a screen, a dark shadow can form. Cardboard is one material used to explore this behaviour in the chapter.

A shadow is observed when an object blocks light from reaching a surface. We therefore need a light source, an opaque object, and a screen. A wall, floor, or the ground can act as the screen in everyday situations.

A shadow forms because the opaque object blocks light. It does not copy the object’s surface colour. Changing only the colour of the object, while keeping the lighting and arrangement unchanged, therefore does not change the shadow’s colour.

With the torch and wall fixed, moving the ball nearer the torch makes it block a wider part of the light reaching the wall. Its shadow becomes larger. Moving the ball closer to the wall makes the shadow smaller.

When light falls on a mirror, the mirror changes its direction. This is called reflection of light. The chapter demonstrates it by using a mirror or shiny steel plate to redirect sunlight onto a wall or another nearby surface.

A plane mirror is flat and forms an erect image, meaning the image is upright. The image is the same size as the object. Moving the object to different positions does not make the mirror form a larger or smaller image.

The chapter’s activity asks us to move a screen in front of and behind a plane mirror. The image cannot be obtained on that screen. We see the image by looking into the mirror, where it appears behind the reflecting surface.

In a plane mirror, the left side appears as the right side of the image, and the right appears as the left. This perceived reversal is called lateral inversion. The image remains upright rather than turning upside down.

A plane mirror produces lateral inversion. Reversing the lettering on the front of an ambulance allows drivers ahead to see the word in its normal form through their rear-view mirrors. This helps them recognise the approaching ambulance more easily.

Light from an object passes through the small hole and forms an image on the screen inside the camera. The image is upside down, or inverted. This differs from the upright image formed by a plane mirror during reflection.

A simple periscope uses two plane mirrors to change the direction of light through reflection. It helps a person see past an obstruction. The chapter mentions uses in submarines, tanks, and bunkers, and for looking beyond taller people.

A kaleidoscope uses three mirror strips arranged together. Light reflects repeatedly between them, producing multiple images of coloured pieces or other objects. Turning the kaleidoscope changes their arrangement and the resulting patterns, which can inspire artists and designers.

A plane mirror causes lateral inversion, but some letters look the same after this reversal. Ordinary upright block letters T and O have matching left and right halves. Their unchanged appearance therefore does not mean that lateral inversion is absent.

The chapter states that light from the Sun takes about eight minutes and twenty seconds to reach Earth. We therefore see sunlight after it has travelled for this time, rather than at the exact moment it leaves the Sun.

Thick cardboard is opaque and blocks light, producing a dark shadow. Tracing paper is translucent, so some light passes through it and the shadow is lighter. The difference comes from how the materials allow or prevent light from passing.

A shadow depends on how an object blocks light reaching the screen. Tilting the cut-out changes the part of its shape presented to the light. The shadow can therefore change even when the cardboard itself keeps the same shape.

Each shadow depends on light from a particular source being blocked by the ball. Switching off one torch removes that source’s shadow pattern. The remaining torch still shines on the ball, so its shadow continues to appear on the wall.

A translucent object lets some light pass through but still prevents some light from reaching the screen. It can therefore produce a lighter shadow. The chapter even notes that some transparent objects can produce faint shadows, so the claim is too broad.

The mirror reflects light and changes its direction. Turning or tilting the mirror changes where the reflected light travels, so the bright spot moves on the wall. This follows the chapter’s activity using a shiny plate or plane mirror.

The chapter describes that a person’s image appears nearer the mirror when the person moves closer to it. The image remains upright and the same size as the person. Its changing apparent position does not change these basic image properties.

A pinhole camera forms an image using light from the object. The image is inverted and can show the object’s colours. This makes it different from an ordinary shadow, which is a dark region formed where an object blocks light.

The pinhole camera forms an inverted image on its screen. A plane mirror forms an upright image that cannot be obtained directly on a screen. Comparing these features helps distinguish the two ways of forming images described in the chapter.

Being visible does not always mean that an object produces light. The glowing firefly emits its own light and is luminous. The leaf becomes visible by reflecting light from the torch, so it is non-luminous in this situation.

Light still travels in straight sections inside a simple periscope. The mirrors change its direction at each reflection, directing it towards the viewer’s eye. This arrangement allows an object to be seen even when a barrier blocks the direct view.