SCIENCE 10-Q2
LIGHT: MIRRORS & LENSES
Week 7
Day 1&2 Optical Instruments
What’s In
In the prvious week, you have learned that mirrors are able to form
images because of regular reflection of light, while lenses form images by
refracting light rays. You have gained concepts on the rules of ray diagrams to
locate and describe the images formed by such optical instruments.
Reflection is the bouncing of llight when it hits a surface, while refraction is the
bending of light rays at the boundary between two different media due to the
difference velocities of light. Both reflection and refraction of light enable some
instruments to form images.
A mirror forms images by regular reflection of light. A lens forms images by
refracting light.
1. What Is It
A Pinhole Camera
The pinhole camera is the simplest kind of camera. It does not have a lens. It
just makes use of a tiny opening (a pinhole-sized opening) to focus all light rays
within the smallest possible area to obtain an image, as clearly as possible. The
simple image formed using a pinhole camera is always inverted.
Images formed by a Pinhole Camera
To understand how a pinhole camera
works, imagine yourself inside a dark room
which allows no light inside. Now imagine a
small opening made on the wall that you are
facing. If someone were to hold a torchlight
from the outside, you could see that light
seep into your room. If the person with the
torch moved around the light source, you
would see the light seeping in, vary in terms
of direction and even intensity.
1
Now instead of a room, imagine a small box with has been light proofed
except for a small pin-sized opening on the box. Instead of you inside, there is a film
which captures light rays. Instead of you looking at the image of light rays hitting the
opposite side of the wall, the film inside the box records the image. The exposure to
the light has to occur for a prolonged period because the pinhole opening limits the
amount of light entering.
A Microscope
A microscope is an instrument that is used to
magnify small objects. Some microscopes can even be
used to observe an object at the cellular level, allowing
scientists to see the shape of a cell, its
nucleus, mitochondria, and other organelles. While the
modern microscope has many parts, the most important
pieces are its lenses. It is through the microscope’s
lenses that the image of an object can be magnified and
observed in detail. A simple light microscope
manipulates how light enters the eye using
a convex lens, where both sides of the lens are curved
outwards. When light reflects off of an object being
viewed under the microscope and passes through the
lens, it bends towards the eye. This makes the object
look bigger than it actually is.
The Optical Telescope
There are two types of telescope, the
refracting telescope or refractors and the reflecting
telescope or the reflectors. A refractor
uses lenses within a tube to refract (bend) light.
It's the type of long telescope which you might
imagine old-time astronomers, like Galileo, using.
Reflectors, on the other hand, use mirrors instead
of lenses to reflect light.
Most modern observatories use reflectors
because their telescopes are so huge. Refractors
would not be practical. Their lenses would be very heavy and their tubes would
need to be very long.
2
The Periscope
A periscope
mirrors to reflect images through a tube. Light from a
distant object strikes the top mirror and is then reflected
at an angle of 90 degrees down the periscope tube. At
the bottom of the periscope, the light strikes another
mirror and is then reflected into the viewer's eye. This
simple periscope uses only flat mirrors as compared to
the periscopes used on submarines, which are usually a
complex optical system using both lenses and mirrors.
What’s New
Activity 1. What Am I? Identify the following optical devices based on the
description given.
____________1. This device may use only flat mirrors or a complex optical
system using both lenses and mirrors to reflect imges through
a tube.
____________2. It uses lenses within a tube to refract (bend) light and is used
in most observatories to get images of some stars.
____________3. It just makes use of a tiny opening (a pinhole-sized opening) to
focus all light rays within the smallest possible area to obtain an
imageof an object placed in front of it.
____________4. is an instrument that is used to magnify small objects.
____________5. Light from a distant object strikes the top mirror and is then
reflected at an angle of 90 degrees down the tube of this
device.
