CBSE Class 7 Science Light and Reflection Worksheet Set 06

Answer: (b) energy. Light is energy that lets us see objects.

Teacher's Note:
1. Light carries energy and can be detected by the eye.
2. Matter has mass, light does not.

Answer: (a) straight line. In a uniform medium light moves along straight lines, which is why shadows have sharp edges.

Teacher's Note:
1. This is called rectilinear propagation of light.
2. It explains how shadows form.

Answer: (a) reflection. Reflection means light is thrown back into the medium it came from.

Teacher's Note:
1. The word comes from reflect, meaning to turn back.
2. Refraction is bending on entering a new medium.

Answer: (b) plane mirror. A polished, smooth surface like a mirror reflects almost all light in a regular way.

Teacher's Note:
1. Rough surfaces such as paper and walls scatter light.
2. A mirror keeps the reflected rays in order.

Answer: (b) virtual and erect. The image cannot be caught on a screen and is the same way up as the object.

Teacher's Note:
1. Virtual images appear to be behind the mirror.
2. They are formed by reflected rays that only seem to meet.

Answer: (a) the same as the distance of the object in front. Object and image are equally far from the mirror surface.

Teacher's Note:
1. If you stand 2 m from a mirror, your image appears 2 m behind it.
2. So you seem 4 m from your image.

Answer: (b) 60°. By the law of reflection, angle of reflection equals angle of incidence.

Teacher's Note:
1. The angles are measured from the normal, not the surface.
2. So both are 60°.

Answer: (a) always. The law of reflection holds for every reflecting surface, smooth or rough.

Teacher's Note:
1. Even in diffused reflection each tiny ray obeys the law.
2. The surface only changes the direction of the normal at each point.

Answer: reflects. A polished surface sends most of the light back.

Teacher's Note:
1. A mirror is made to reflect rather than absorb light.
2. Black surfaces absorb more.

Answer: blocked (stopped). The dark region behind the object receives no direct light.

Teacher's Note:
1. An opaque object does not let light pass through it.
2. The dark area behind it is the shadow.

Answer: real. Real images are formed where light rays actually meet.

Teacher's Note:
1. Real images can be projected on a screen.
2. A plane mirror cannot form one.

Answer: incidence. It is measured from the normal at the point where the ray strikes.

Teacher's Note:
1. The normal is an imaginary line at 90° to the surface.
2. Both angles of reflection are measured from it.

Answer: virtual. Light does not actually reach the place where the image seems to be.

Teacher's Note:
1. Virtual images are seen only by looking into the mirror.
2. A screen placed behind a plane mirror stays blank.

Answer: False. A plane mirror forms a virtual image.

Teacher's Note:
1. The image lies behind the mirror where no light actually goes.
2. So it cannot be shown on a screen.

Answer: True. This is lateral inversion.

Teacher's Note:
1. The mirror swaps left and right.
2. Up and down stay the same.

Answer: False. Diffused reflection from rough surfaces is what lets us see most objects from any direction.

Teacher's Note:
1. Light scatters in many directions from a rough surface.
2. That is why a wall can be seen from every side.

Answer: False. The image is exactly the same size as the object.

Teacher's Note:
1. A plane mirror neither enlarges nor reduces.
2. The image only appears reversed left to right.

Answer: False. It is called the reflected ray; the incident ray is the one that strikes the surface.

Teacher's Note:
1. The incident ray goes in and the reflected ray comes out.
2. Remember this pair to label diagrams.

Answer: 1. The angle of incidence is equal to the angle of reflection.
2. The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane.

Teacher's Note:
1. Both laws are true for any reflecting surface.
2. Angles are always measured from the normal.

Answer: Regular reflection takes place from a smooth, polished surface and the reflected rays stay parallel, so clear images are formed. Diffused reflection takes place from a rough surface and the reflected rays go in many directions, so no clear image forms.

Teacher's Note:
1. A mirror shows regular reflection and a sheet of paper shows diffused reflection.
2. Both obey the laws of reflection.

Answer: 1. The image is virtual.
2. It is erect.
3. It is of the same size as the object.
4. It is as far behind the mirror as the object is in front, and it is laterally inverted.

Teacher's Note:
1. These are four of the main features to remember.
2. Any four correct ones earn full marks.

Answer: Lateral inversion is the reversal of left and right in the image formed by a plane mirror. The word is painted reversed so that a driver ahead, looking in the rear-view mirror, reads it correctly and gives way.

Teacher's Note:
1. The mirror reverses the reversed letters back to normal.
2. This helps drivers recognise an ambulance quickly.

Answer: 1. In homes and shops to see our own image.
2. In periscopes and kaleidoscopes.
3. As rear-view mirrors and in dressing tables or barber shops.

Teacher's Note:
1. Uses based on formation of images and on reflection are accepted.
2. Name any three.

Answer: A periscope is a device used to see objects that are not in the direct line of sight, such as from a submarine or over a crowd. It has two plane mirrors fixed parallel to each other, each at 45° to the tube, and works on repeated reflection of light.

Teacher's Note:
1. Light is reflected from the top mirror to the bottom mirror and then to the eye.
2. The final image is erect.

Answer: Angle of incidence = angle of reflection, and together they make 70°.
So angle of incidence = 70° ÷ 2 = 35°.

Teacher's Note:
1. The angle between the two rays is the sum of both angles.
2. Divide by two because they are equal.

Answer: The letters A, H, I, M, O, T, U, V, W, X and Y look the same, because they are symmetrical about a vertical line.

Teacher's Note:
1. A mirror swaps left and right only.
2. Letters that are left-right symmetric stay unchanged.

Answer: Luminous but not hot: a firefly and a tube light (or an LED). Non-luminous: a book and the Moon, which only reflect light.

Teacher's Note:
1. Luminous objects produce their own light.
2. Non-luminous objects are seen only because they reflect light.