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Method:

  1. Using the same arrangement as in Experiment Lenses B, place the object (candle) at the distance indicated from the lens.
  2. Move the screen until a clear sharp image is obtained. Record the results on the table below.

Results:

f = focal length of lens d 0 = object distance d i = image distance

Object distance Image distance 1 d 0 1 d i 1 d 0 + 1 d i
d 0 (cm) d i (cm) (cm - 1 ) (cm - 1 ) (cm - 1 )
25,0
20,0
18,0
15,0
Average =        
Reciprocal of average = 1 1 d 0 + 1 d i = ̲ ( a ) Focal length of lens = ̲ ( b )

QUESTIONS:

  1. Compare the values for (a) and (b) above and explain any similarities or differences
  2. What is the name of the mathematical relationship between d 0 , d i and f ?
  3. Write a conclusion for this part of the investigation.

Drawing Ray Diagrams for Converging Lenses

Ray diagrams are normally drawn using three rays. The three rays are labelled R 1 , R 2 and R 3 . The ray diagrams that follow will use this naming convention.

  1. The first ray ( R 1 ) travels from the object to the lens parallel to the principal axis. This ray is bent by the lens and travels through the focal point .
  2. Any ray travelling parallel to the principal axis is bent through the focal point.
  3. If a light ray passes through a focal point before it enters the lens, then it will leave the lens parallel to the principal axis. The second ray ( R 2 ) is therefore drawn to pass through the focal point before it enters the lens.
  4. A ray that travels through the centre of the lens does not change direction. The third ray ( R 3 ) is drawn through the centre of the lens.
  5. The point where all three of the rays ( R 1 , R 2 and R 3 ) intersect is the image of the point where they all started. The image will form at this point.

In ray diagrams, lenses are drawn like this:

Convex lens:

Concave lens:

CASE 1: Object placed at a distance greater than 2 f From the lens

An object is placed at a distance greater than 2 f away from the converging lens. Three rays are drawn to locate the image, which is real, and smaller than the object and inverted.

We can locate the position of the image by drawing our three rays. R 1 travels from the object to the lens parallel to the principal axis, is bent by the lens and then travels through the focal point. R 2 passes through the focal point before it enters the lens and therefore must leave the lens parallel to the principal axis. R 3 travels through the center of the lens and does not change direction. The point where R 1 , R 2 and R 3 intersect is the image of the point where they all started.

The image of an object placed at a distance greater than 2 f from the lens is upside down or inverted . This is because the rays which began at the top of the object, above the principal axis, after passing through the lens end up below the principal axis. The image is called a real image because it is on the opposite side of the lens to the object and you can trace all the light rays directly from the image back to the object.

The image is also smaller than the object and is located closer to the lens than the object.

In reality, light rays come from all points along the length of the object. In ray diagrams we only draw three rays (all starting at the top of the object) to keep the diagram clear and simple.

Questions & Answers

how do we convert atm to pa
mpho Reply
what is a mole?
Tefo Reply
The mole is the SI unit for an amount of substance
Lindo
K.Thanks
Tefo
mole is the amount of a substance having the same number of particles as there are atoms in 12g carbon-12
mpho
what is STP. I m still confused
Serati Reply
Standard Temperature and Pressure
mpho
what is the difference between an ideal and real gases
Denzel Reply
. the particles of the glass are free to move and thus often collide with other particles as well as themselves when contained. an ideal gas is a term describing a gas that's particles when colliding with other particles don't lose energy, no change in the particles kinetic energy after thecollision
Courtney
The number of HCl molecules in 16 mol
Prosperity Reply
what is ionic atom
Sebabatso Reply
how does newtons third law meet with electronics
Moipone Reply
what is the formula of Newton's first law?
John Reply
f=ma
Oriphulusa
ohk
Moipone
ma
Koketso
the newton first law of motion is the object start moving slower and the formula f=m/a
Asali
M - mass & a - acceleration
Kagiso
determine the molecular formula if the molar mass of the compound is 282 g .mol
Mmatsatsi Reply
if a person what learn for music what studies can that person follow
Kruger Reply
What is friction?
Letlhogonolo Reply
when one object rub against each other they cause friction
Daniel
a force to which opposes the motion of a object. this force unlike gravity depends on the motion of the object /the path that it takes. this is called a non conventional force
Courtney
what is ohms
Xolile Reply
ohm is an unit to measure the electrical ressistance of a conductor(generally metalic and a few non metallic)
Mani
A device that bars the passage of an electric charge between two points.
Mike Reply
a conductor such as wire
Courtney
what is a resistor
Queentin Reply
it's a substance such a metal that has valent electrons. when current is past through this metal will cause an obstruction to the flow of the electrons. this obstruction to the flow of electrons causes a dip in the potential energy of the electrons which results in what we know as potential diff
Courtney
georg ohm basically just used the term resistance to describe the relationship between the potential differnce and current in a conductor
Courtney
what is a emf?
Gaone Reply
electromotive force. it's basically the measurement of the energy that causes current to flow. a battery may have a emf of 12v meaning it can convert its chemical evergy and output 12v of electrical energy
Courtney

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Source:  OpenStax, Siyavula textbooks: grade 11 physical science. OpenStax CNX. Jul 29, 2011 Download for free at http://cnx.org/content/col11241/1.2
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