Class 7 Science Chapter 11 Light: Shadows and Reflections

Why does a kaleidoscope produce different patterns when rotated slightly?

The angle of reflection changes, creating new patterns

During a lunar eclipse, the Earth blocks sunlight from reaching the Moon. Why does this make the Moon temporarily invisible?

No sunlight reaches the Moon to reflect back to Earth.

If an object is placed 5 meters in front of a plane mirror, how far behind the mirror does the image appear to be?

5 meters

Why does a kaleidoscope show multiple images of the objects inside?

Due to multiple reflections between the three mirrors

If you stand 2 meters away from a plane mirror, how far does your image appear to be from the mirror?

4 meters

Three pinholes are made in a cardboard sheet such that they are aligned in a straight line. A torch is placed on one side of the cardboard and a screen is placed on the other side. What will happen to the light spot on the screen if the middle pinhole is moved slightly upward?

The light spot disappears.

An opaque object is placed at a distance $d$ from a point light source and forms a shadow on a screen placed at a distance $D$ behind the object. If the object is moved closer to the light source by $\frac{d}{2}$, how does the size of the shadow change? Assume the screen remains fixed.

The shadow size increases but not necessarily doubles

What would you observe on the screen if the candle flame is moved closer to the pinhole in Activity 11.9?

The image becomes larger and inverted

What happens when light traveling inside a glass block (refractive index 1.5) strikes the glass-air interface at exactly the critical angle? Consider both reflection and refraction phenomena.

Refracted ray grazes the surface while most light reflects

A point source of light is placed 3 meters away from an opaque square-shaped object of side 20 cm. The screen is placed 1 meter behind the object. What will be the approximate size of the shadow formed on the screen?

27 cm

If the distance between the pinhole and screen is doubled in a sliding pinhole camera made of two boxes, how does the size of the image change while keeping the object distance constant?

The image size doubles.

Why would someone choose oiled paper over clear glass for a bathroom window?

To allow light while maintaining privacy

In a kaleidoscope with three mirrors arranged in an equilateral triangle, how many images of a single bead will be formed if each mirror reflects the other two mirrors infinitely?

5

A student observes the following objects at night: Moon, LED lamp, Venus, and a burning candle. Which combination correctly classifies these objects as luminous or non-luminous?

Moon (Non-luminous), LED lamp (Luminous), Venus (Non-luminous), burning candle (Luminous)

In a setup where an LED lamp (point source) and a candle (extended source) are placed at the same distance from an opaque object, what difference will be observed in their shadows when projected on a screen?

The LED's shadow will be sharp and well-defined, while the candle's will be fuzzy.

How would using a polished metal pipe instead of a flexible opaque pipe affect the visibility of the candle flame when the pipe is bent?

The flame would remain visible even when the pipe is bent sharply

When an opaque object blocks sunlight, a shadow is formed on the screen. If the same object is replaced with a shiny steel plate, what additional observation can be made?

A bright spot appears along with the shadow

Which of these is an advantage of LED lamps?

They last longer than traditional lamps

If an object is placed 5 meters away from a plane mirror, how far behind the mirror will its image appear to be?

5 meters

A periscope is constructed with two plane mirrors placed at a 45-degree angle each in a Z-shaped box. If light enters the periscope horizontally from an object located 5 meters away, what is the total distance traveled by the light inside the periscope before it exits to the observer’s eye?

15 meters

A student observes an object labeled “ABC” through a pinhole camera and a plane mirror. Which of the following correctly describes the nature of the images formed?

The image in the plane mirror is CBA, and in the pinhole camera, it is $\text{C}^\prime\text{B}^\prime\text{A}^\prime$.

A periscope is constructed using two plane mirrors placed at 45° angles inside a Z-shaped tube. If the light enters the periscope horizontally from the left, what will be the angle of reflection at the second mirror when the light exits the periscope vertically upwards?

45°

In Activity 11.3, if you replace the cardboard with a glass sheet, what would be the outcome?

Light will pass fully, forming a bright spot

If an object is placed 5 meters away from a plane mirror, how far behind the mirror does the image appear to be?

5 meters

Which of the following materials would allow partial passage of light when placed between a torch and a screen?

Tracing paper

A translucent rectangular sheet and an opaque rectangular sheet of the same dimensions are placed one after another in front of a point light source and a screen. What will be observed on the screen?

A dark shadow with a faint outer region

Why does the pattern in a kaleidoscope change when it is rotated?

The reflection angles change

An opaque square block is moved progressively closer to a point light source while keeping the screen fixed. What happens to the sharpness and size of the shadow as the object approaches the light source?

The shadow becomes larger and sharper.

Why is the image formed by a pinhole camera inverted?

Because light travels in straight lines and crosses at the pinhole

Which of the following is an example of an artificial light source?

Oil lamp

What does passing a laser beam through a beaker filled with water (containing a drop of milk) demonstrate?

Light travels in a straight line.

When you raise your right hand in front of a plane mirror, what does the image appear to do?

Raises its left hand

An object is placed 5 meters in front of a plane mirror. How far behind the mirror is the image formed?

5 meters

An opaque object is placed between a point source of light and a screen. The object is moved closer to the screen while keeping the position of the light source fixed. What happens to the size of the shadow formed on the screen?

The size of the shadow increases

What happens when you rotate the kaleidoscope slightly while peeping through it?

A completely new pattern is observed each time

A person stands in front of a plane mirror and writes the number “1961” on a board parallel to the mirror. How will the image of the number appear in the mirror?

1691

An experiment is conducted where a torch is kept at a fixed distance from a screen. A translucent object is placed between the torch and the screen. What will happen to the shadow’s characteristics if the object is replaced with an opaque one of the same shape and size?

The shadow remains the same size but becomes darker

What is a major consequence of light pollution on fireflies?

Disruption in communication

An object made of frosted glass is placed between a point light source and a screen. What will be the nature of the shadow formed on the screen?

Light and blurry

Which of the following letters will NOT appear laterally inverted when reflected in a plane mirror?

A

A circular opaque disc is placed between a point light source and a screen. The disc is tilted at an angle of 45 degrees with respect to the incident light. What will be the shape of the shadow observed on the screen?

Ellipse \triangle Right Triangle

(A) The Moon is a non-luminous object.
(R) The Moon reflects the light emitted by the Sun.

Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Which of these is a natural source of light?

Firefly

In which of the following scenarios would a periscope NOT be useful?

Observing distant stars through a telescope

Why can you see a candle flame through a straight pipe but not through a bent pipe?

Light cannot change direction to follow the bent pipe

A red opaque square is placed in front of a white screen, and a white light source illuminates it. The red square is then replaced with a blue opaque square of the same size and shape. How does the shadow on the screen change?

The shadow remains black and unchanged in size

In an experiment, a laser beam is passed through four different materials: clear glass (A), frosted glass (B), thick cardboard (C), and water with milk droplets (D). The beam was observed from the side of each material. Through which materials would the path of laser beam be most clearly visible from the side?

Only D
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