SECTION 01

(a)(i) State two ways in which the image formed in plane mirror differ from that in a pin hole camera.

Hint diagrams:

Image formation by plane mirror 

Image formation by pin hole camera 

Answer:

Image formation: Image formed by plane mirror is virtual this is due to virtual intersection of rays of light beyond the mirror during image formation BUT the image of pin hole camera is formed by actual intersection of rays of light after passing the pin hole.

Image orientation: Image formed by plane mirrors are of the same size as the object with the same distance from mirror as the object and are lateral inverted BUT image formed by the pin hole camera is upside down, vertical inverted and can have different sizes based on distance between object and the pinhole or pinhole and the screen.

(ii) What is the effect of moving the pinhole camera closer to the object?

Increase of image formed, the close the pinhole camera moves towards the object the larger the image formed on the screen due to intersection of light beams.

SECTION 02

(b)(i) List three rules used to locate images in curved mirrors

Hint diagrams:

Path of rays for curved mirrors 

Answer:
1. Any incident ray traveling parallel to the principal axis­ on the way to the mirror will pass through the focal point upon reflection.

2. Any incident ray passing through the focal point on the way to the mirror will travel parallel to the principal axis upon reflection.

3. Any incident ray forms an equal angle to the reflected ray on the tangent line at point of intersection between principal axis and the curved mirror.

(ii) Give two similarities and two differences that exist between the human eye and lens camera

Eye versus camera 

SIMILARITIES

1. The shutter in a camera can be compared to the iris in a human eye. It controls how much light is able to enter the lens.

2. The lens in a camera is similar to the lens in the human eye, which are both used to focus light and create an image.

3. With a camera, an image is recorded on a film. In the human eye, the image is formed on the retina.

DIFFERENCES

1. Eye uses live cells to detect light while the camera uses a diaphragm to detect light and capture images.

2. Stereoscopic vision of eyes allows 3 dimensional images while camera captures only 2 dimensional images.

3. The pupil adjusts the size while focusing while in a camera lens moves to change focus.

4. Eyes have blind spots while cameras do not.

SECTION 03

(c) (i) A mirage is often seen by a motorist as a pool of water on the road some distance ahead

Draw a sketch diagram to show the formation of such a mirage

Mirrage formation  

(ii) Briefly explain how mirage is formed

Mirage is an optical illusion which occurs usually in deserts on hot summer days due to atmospheric refraction and total internal reflection of light rays. In mirage, the object such as a tree appears to be inverted as if it is situated on a bank of a pond of water. Actually, on a hot summer day, the layers of air near the surface of earth become very hot and hence behave as optically rarer medium. On the other hand, the upper layers of air are comparatively cool and hence behave as optically denser medium. Now, a ray of light from the point T of a tree goes from denser to rarer medium along the path TB and bends away from the normal, at every layer due to atmospheric refraction. But at a particular layer, when the angle of incidence becomes greater than the critical angle, the total internal refraction occurs, and the totally reflected ray travels along the path BE and reaches the observer. Since, we can see the light rays only in straight line path, so the reflected ray BE appearing to be coming from the point T’ to the observer. Due to this, an inverted image of the tree is formed below its actual position. And this inverted image of the tree creates the impression as if the reflection of tree is taking place from a pond full of water.

Mirrage formation due to density variation