Documents.mx Chapter 5 Light Teachers Guide 558445afb6f9e

8/18/2019 Documents.mx Chapter 5 Light Teachers Guide 558445afb6f9e

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JPN Pahang Physics Module Form 4Chapter 5 Light

CHAPTER 5: LIGHT

In each of the following sentences, fill in the rac!et the appropriate word or words gi"en elow#

solid, liquid, gas, vacuum, electromagnetic wave, energy

$# Light is a form of %

'# It tra"els in the form of % &

(# In can tra"el through % &

4# It tra"els fastest in the medium of % &

5# Light of different colours tra"els at the same speed in the medium of % &

Light allows us to see o)ects#

Light can e reflected or refracted#

5.1 UNDERSTANDING REFLECTION OF LIGHT

Plane mirror and refle!ion* In the o+es pro"ided for the diagram elow, write the name of each

of the parts indicated#

La"# of Refle!ion* tate the laws of reflection#

%i& -----------------------------------#

---------------------------------##

--#

%ii& -----------------------------------##

Plane mirror

Incident ray Reflected ray

Normal Reflected angle Incident angle

Point of incidence

i r

ir

Plane mirror

$

energy Electromagnetic wave

Solid, liquid, gas and vacuumvacuum

vacuum

The incident ray, the reflected ray and the normal to the point of incidence, all lie in the

same plane.

The angle of incidence, i The angle of reflection, r


2/38


-----------------------------------#

#

E$eri#e 1. .he diagram elow shows how the relationship etween incident angle and reflected

angle can e in"estigated#

Fill in the "alues of the angles of reflection, r in the tale elow

E$eri#e %:

E$eri#e &*

/FF

/N

i r

/FF

/N

i r

ir $0!"'0#"(0$"40%"50&"

mirror mirror

Laser pen

Laser pen

Mirror

50o

θ

o

normal

/riginal direction

d

1ased on the diagram on the left,

calculate the angle, θ # 2encedetermine the angle of de"iation, d #

θ %"o

d '"o

'


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Ima'e formed () a *lane mirror* 3sing the law of reflection, complete the ray diagram to

determine the position of the image#

hat can you say aout the line )oining o)ect and image ---------------

hat can you say aout the distances 61 and 1C ------------------##

Differene# (e!"een real and +ir!,al ima'e*

Mirror eforerotation

Mirror rotated θ o

7eflected ray afterrotation

Incident ray 7eflected ray eforerotation

n o r m a l

α

θ

1ased on the diagram ao"e, when the mirror is rotated an angle,θ , without changing

the incident ray, what is the angle rotated,α , for the reflected ray in terms of θ

α #θ

o)ect

i$

r $

6 1 C

8ye

Image

(

Perpendicular to the mirror

() )*


4/38


C-ara!eri#!i# of ima'e formed () *lane mirror* /ser"e the pictures elow as well as using

pre"ious !nowledge, list the characteristics#

E$eri#e 1*

E$eri#e %*

7eal image9irtual imageCan e caught on a

screenCannot e caught on a screenFormed y the

meeting of real rays#Form at a position where rays

appear to e originating#

m i r r o r

o)ect image

i& virtual

ii& laterally inverted

iii& same si+e as o-ect

i"& o-ect distance

image distance

Complete the ray diagram elow consisting of ' rays originating from the o)ect, reflected

and entering the eye such that the eye sees the image#

o)ect8ye

Mirror

4


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E$eri#e &*

ACTIIT/* Find out some of the uses of plane mirrors %application of reflection

6hmad is mo"ing with speed ' m s:$ towards a plane mirror# 6hmad and his image will

approach each other at

$ m s:$

' m s:$

( m s

:$

4 m s:$

Four point o)ects 6, 1, C and ; are placed in front of a plane mirror MN as shown# 1etween their

images, which can e seen y the eye

M N

6 1 C ;

8ye

image image * image )image (

/nly image can e seen ecause the line -oining image to the eye cuts the

actual mirror

5


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C,r+ed 0irror#*

Terminolo')* 7efer to the diagrams ao"e and gi"e the names for the following*

Effe! of ,r+ed mirror# on iniden! ra)#*

a& Iniden! ra)# *arallel !o !-e *rini*al a$i#*

tudy the diagrams ao"e and fill in the lan!s for the following sentences#

r < ' f

PC

r

Concave mirror

C

r

P

Convex mirror

C = Centre of curvature r = Radius of curvature P = Pole PC = Principal axis

Concave mirror Convex mirror

PC

r

f

F CP

r

F

f

Rays parallel to the principal axis converge at the ……………………, F F is positioned at the ………………….. between C and P FP is named the ………………………… which is denoted by f .

Hence write an equation giving the relationship between r and f .

Principal focus

0id point

1ocal length

=


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& Iniden! ra)# *arallel !o ea- o!-er (,! no! *arallel !o !-e *rini*al a$i#*

tudy the diagrams ao"e and fill in the lan!s in the following sentences#

Parallel rays con"erge at a point called -----------

.he focal plane )oins F, the principal focus and all ----------##and is

---------# to the principal a+is

.he ray passing through C is reflected ac! along the line of the--------#ray#

.he distance etween the focal plane and the mirror is the ----------#, f #

Ima'e formed () ,r+ed mirror %ray diagram method&

Prini*le of dra"in' ra) dia'ram#*

a. Ra)# *arallel !o !-e *rini*al a$i# are refle!ed !-ro,'- !-e *rini*al fo,# F.

PC

r

f

F

Focal plane

CP

r

F

f

Focal plane

Cona+e mirror Con+e$ mirror

PC F P CF


>

secondary focus

secondary foci

perpendicular

incident

focal length


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E$eri#e 1* Complete the ray diagrams elow*

(2 Ra)# *a##in' !-ro,'- !-e *rini*al fo,# are refle!ed *arallel !o !-e *rini*al a$i#.

E$eri#e %* Complete the ray diagrams elow*

2 Ra)# *a##in' !-ro,'- !-e en!er of ,r+a!,re are refle!ed dire!l) (a3.

PC F P CF


PC F P CF


PC F P CF


PC F P CF


?


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E$eri#e &* Complete the ray diagrams elow*

Ima'e formed () ona+e mirror:

3sing the principles of construction of ray diagram, complete the ray diagrams for each of the cases

shown elow*

u < o)ect distance @ v < image distance @ f < focal length @ r < radius of cur"ature

Ca#e 1: u 4 % f

2ence state the characteristics of image formed*

i& ii& iii&

Ca#e %: u % f or u = r

Characteristics of image formed*

i& ii& iii&

PC F P CF


C Fimage

C FF

o)ect

Conca"e mirror

image

A

Fo)ect

Conca"e mirror

diminished real inverted

ame siBe real inverted


10/38


Ca#e &: f 6 u 6 % f


i& ii& iii&

Ca#e 7: u f


i&

Ca#e 5: u 6 f


i& ii& iii&

C F F

o)ect

Conca"e mirror

image

C FF

o)ect

Conca"e mirror

C FF

o)ect

Conca"e mirror

image

$0

magnified real inverted

Image at infinity

magnified virtual upright


11/38


Ima'e formed () on+e$ mirror: %using construction of ray diagram

u < o)ect distance @ v < image distance @ f < focal length @ r < radius of cur"ature


i& ii& iii&

U#e# of ,r+ed mirror#*

Ne"!on8# Tele#o*e* Fill in the o+es the type of mirror used

C FF

o)ectConca"e mirror

image

Concave mirror

Plane mirror

Eye

Lens

OOFF

here should the lamp e placed to achie"e the

ao"e result (t the principal focus

Car -ead lam*Cur"ed mirror

lamp

$$

diminished virtual upright


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A!i+i!)* Find more uses of cur"ed mirrors#

$'


13/38


5.% UNDERSTANDING REFRACTION OF LIGHT

hat is the phenomenon which causes the ending of light in the picture ao"e

---------------------------------------

-

hy did this ending of light occur %thin! in terms of "elocity of light&

---------------------------------------

-

Refra!ion of li'-!*

Fill in each of the o+es

the name of the part shown

air

water

$(

i

i

r

r

lass

Air

Air

refraction

The velocity of light changes when it travels from one medium into another

Incident ray Incident angle Normal

Refracted angle

Refracted ray

Emergent angle Emergent ray


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Dire!ion of refra!ion*

;raw on the diagrams ao"e the appro+imate directions the refracted rays#

hen light tra"els from a less dense medium to a denser medium, the ray is refracted9!o"arda"a) from2 the normal at point of incidence#

hen light tra"els from a more dense medium to a less dense medium, the ray is refracted

9!o"arda"a) from2 the normal at point of incidence#

Snell8# la"*

nellDs law states that --------------------

hat is the name and symol of the constant ----------##

E$eri#e 1*

7eferring to the diagram on the right,

Calculate the refracti"e inde+ of liEuid:#

( )( )0

0

(0sin

=0sin=n

!.2$#

$4

6ir

LiEuid:

=0o

(0o

Less densemedium

;enser

medium

densermedium

Less dense

medium

normal normal

The ratio of sin3angle of incident4 to sin3angle of refraction4 is a

constant

i.e.( )

( )

constant

sin

sin=

anglerefracted

angleincident

Refractive inde5, n


15/38


E$eri#e %*

7eferring to the diagram on the right,

Calculate the refracti"e inde+ of liEuid:G#

n !.%!%

E$eri#e &*

/n the diagram to the right, draw two rays

which originate from the fish to show

how a person oser"ing from ao"e

the surface of the water is ale to see the

image of the fish at an apparent depth

less than the actual depth of the fish#

E$eri#e 7*

6n eEuation that gi"es the relationship etween apparent depth, real depth and the refracti"e inde+

of water for the diagram ao"e is

depthapparent

depthreal=n

If the fish is at an actual depth of 4 m and the refracti"e inde+ of water is $#((, what is the apparentdepth of the image

(pparent depth $ m

$5

6ir

water

8ye

6ir

LiEuid:G

45o

(0o

o)ect

image


16/38


5.& UNDERSTANDING TOTAL INTERNAL REFLECTION OF LIGHT

Cri!ial an'le and !o!al in!ernal refle!ion*

Figures a, and c show rays eing directed from liEuid:G which is denser than air towards the air

at different angles of incident,θ#

6mong the figures a, and c, only Figure a

has a complete ray diagram#

%i& Complete the ray diagrams for

Figure and Figure c#

%ii& .he angle, * is called --------#

%iii& .he phenomenon which occurs in

Figure c yang is called

--------------#

%i"& tate ' conditions which must e satisfied in order for the phenomenon

you mentioned in %iii& to occur#

---------------------------------

---------------------------------

E$eri#e 1*

7eferring to figure d and using nellDs law,

write an eEuation that gi"es the relationship

etween the critical angle, * , the refracted angle

and the refracti"e inde+ of liEuid:G

( )*

nsin

$=

$=

6ir

LiEuid:G

θ H C

Figure a

6ir

LiEuid:G

A0o

C

Figure

6ir

LiEuid:G

θ *

Figure c

6ir

LiEuid:G

A0o

*

Figure d

*ritical angle

Total internal reflection

6ight must travel from denser medium to less dense medium

The angle of incident must e greater than the critical angle

Partial reflection

.otal reflection


17/38


E$eri#e %*

7eferring to Figure e, determine the

refracti"e inde+ of liEuid:

( )0(0sin$

=n

< '

E$eri#e &*

8+plain why a pencil partially immersed in water loo!s ent#%3se a ray diagram

E$eri#e 7*

Complete the path of the ray in the diagram elow and e+plain how a mirage is formed#

uring the day, the ground is heated y the sun. The layer of air near the ground is hotter than the

layers aove. 7ot air is less dense than cool air. Therefore ray from o-ect is refracted away from

the normal. 8hen angle of incident ecomes larger than the critical angle, total internal reflection

occurs. Thus a mirage is formed.

$>

6ir

LiEuid:

A0o

(0o

Figure e

Layer of hot air

Layer of cool air

8ye

o)ect

8ye

image

ground

Image

3mirage4

i 9 *


18/38


E$eri#e 5*

Completing the ray diagram elow, to show how a periscope wor!s* %critical angle of glass < 4'o&

$?

8ye

lass prism/)ect %&oTotal internal reflection

ta:es place ecause

angle of incident 9

critical angle


19/38


5.7 UNDERSTANDING LENSES

T-in Len#e# *

T)*e# of len#e# * Name the types of lenses shown elow#

%i&

%ii&

Forma!ion of a on+e$ len# and !erminolo'): name the parts shown

Forma!ion of a ona+e len# and !erminolo'): name the parts shown

$A

a# )iconve5 # Plano;conve5 c# *onve5 meniscus

a# )iconcave # Plano;concave c# *oncave

Principal a5is

*entre of curvature

/ptic centre

/ptic centre

Principal a5is

*entre of curvature


20/38


Refra!ion of ra)# *arallel !o !-e *rini*al a$i# of a on+e$ len#*

;raw in the following diagrams the paths of the rays after passing through the lens#

rite in the o+ed pro"ided, the name of the point or line shown#

i&

ii&

iii&

i"&

'0

1ocal plane

Secondary focus

Principal focus

Principal focus

1ocal plane

Secondary focus

F

F

F

F


21/38


Prini*le# of on#!r,!in' ra) dia'ram#* Complete the path of each ray after passing through the

lens

i& ii& iii&

i"& "& "i&

"ii& "iii&

E$eri#e 1*

tate the meaning of each of the following terms*

i& Focal length , f * The distance etween optic centre and the principal focus

ii& /)ect distance, u * The distance etween the o-ect and optic centre

iii& Image distance, v * The distance etween the image and the optic centre

E$eri#e %*

;escrie how you would estimate the focal length of a con"e+ lens in the school la#

Place the lens facing the window on the far side of the la. (d-ust the distance of a screen ehind

the lens until a sharp image of the window is formed. 0easure the focal length 3distance etween

the lens and the image4.

'$

F

F

F

F

F

F

F

F

F

F

F

F

F

F F

F


22/38


C-ara!eri#!i# of ima'e formed () a on+e$ len# * %Construction of ray diagram method&

Construct ray diagrams for each of the following cases and state the characteristics of the image

formed#

i2 Ca#e 1 * u 4 % f where u < o)ect distance @ and f < focal length of lens#

Characteristics of image*

iminished, real and inverted

ii2 Ca#e % * u % f


Same si+e, real and inverted

iii2 Ca#e & * % f 4 u 4 f


0agnified, real and inverted

''

F

F

'F

o)ect

Lens

F

F

'F

o)ect

Lens

F

F

'F

o)ect

Lens

image

image

image


23/38


i+2 Ca#e 7 * u = f


Image at infinity

+2 Ca#e 5 * u < f


0agnified, virtual, upright

E$eri#e*

In each of the following statements elow, fill in the space pro"ide one of the following conditions#

% u 9 #f < #f u < #f 9 u 9 f < u 9 f < u = f &

i& .o otain a real image, the o)ect must e placed at a distance u such that - u 9 f ---

ii& .o otain a "irtual image, the o)ect must e placed at a distance u such that u = f ---

'(

F

F

'F

o)ect

Lens

'F

o)ect

Lens

F

F

image


24/38


C-ara!eri#!i# of ima'e formed () ona+e len# * %y construction of ray diagrams &

Construct a ray diagram for each of the following and state the characteristics of the image formed

i&


iminished, virtual, upright

ii&

Characteristics of image * iminished, virtual, upright

No!e* Image formed y a conca"e lens is always diminished, "irtual and on the same side of the

lens as the o)ect#

Po"er of a len# 9 p2

.he power of the lens is gi"en y*

Power of lens <length focal

$

Si'n on+en!ion %for focal length& and the #I# unit for power of a lens#• .he focal length of a con"e+ lens is % positi"eKnegati"e&

• .he focal length of a conca"e lens is %positi"eKnegati"e&

• .he #I# unit for the power of a lens is- ioptre-and its symol is- -

• hen calculating the power of a lens, the unit of the focal length must e in % mKcm&

E$eri#e 1 * 6 conca"e lens has a focal length of $0 cm# hat is its power

f p

$= <

$#0

$− < :$0 ;

'4

F

F

'F

o)ect

Lens

F

F

'F

o)ect

Lens

image

image


25/38


E$eri#e % * .he power of a lens is 5 ;# tate whether it is a con"e+ lens or a conca"e lens and

calculate its focal length#

*onve5 lens#

f < '0 cm

Linear 0a'nifia!ion 9m2 *

;efinition* Linear ma'nifia!ion <o)ectof height

imageof height

0h

hm i=

1ased of the definition ao"e and the ray diagram elow, deri"e an e+pression for the relationship

etween linear magnification, m, the o)ect distance, u and the image distance, v#

.he triangles, 61/ and ;C/ are similar triangles#

.herefore,u

v

h

hi=

0

.herefore,u

vm =

Len# form,la *

.he relationship etween the o)ect distance, u, image distance, v, and the focal length, f, of a lens

is gi"en y

f vu

$$$=+

• .his lens formula is "alid for oth con"e+ and conca"e lenses#

hen using the len# form,la, the real i# *o#i!i+e #i'n on+en!ionD must e followed#

'5

v

hi

u

ho

Lens

6

1

/ C

;


26/38


.he rules stated in this sign con"ention are*

$& The focal length of a conve5 lens is positive while the focal length of a concave lens is negative

'& /-ect distance is positive for real o-ect> o-ect distance is negative for virtual o-ect

(& Image distance is positive for real image? image distance is negative for virtual image

A**lia!ion of !-e len# form,la*

E$eri#e 1# 6n o)ect is placed $0 cm in front of a con"erging lens of focal length $5 cm#

Calculate the image distance and state the characteristics of the image formed#

f vu

$$$=+

$5

$$

$0

$=+

v

$0

$

$5

$$−=

v

v ; $" cm

Image is virtual

E$eri#e % * 6n o)ect is placed (0 cm in front of a con"erging lens of focal length '5 cm#

a& Find the position of the image, and state whether the image is real or "irtual#

& Calculate the linear magnification of the image#

'5

$$

(0

$+=

v

v !&" cm > Image is real

m v


27/38


6 lens acts as a magnifying glass when the o)ect is placed as in case 5 on page '(#

i& 6 magnifying glass consists of a %on+er'in' di+er'in'& lens#

ii& .he o)ect must e placed at a distance %more !-an f #ame a# f le## !-an f (e!"een

f and % f more !-an % f & in order for the lens to act as a magnifying glass#

iii& .he characteristics of the image formed y a magnifying glass are yang %real +ir!,al& @

%in+er!ed ,*ri'-!& @ %ma'nified dimini#-ed& @ %on !-e #ame #ide a# !-e o(;e! on

!-e o**o#i!e #ide of !-e o(;e!

i"& reater magnification can e otained y using a lens which has % lon' #-or!& focal

length#

Complete the ray diagram elow to show how a magnifying glass produces an image of the

o)ect#

E$eri#e 1 * 6 magnifying glass produces an image with linear magnification < 4# If the power of

the lens is $0 ;, find the o)ect distance and image distance#

u

v=4 uv 4=∴

f $$0 = $0=∴ f cm

$0

$

4

$$=+

uu

5#$'=∴u cm

v &" cm

E$eri#e %: hich of the following lenses with their powers gi"en elow ma!es the magnifying

glass with the highest power of magnification

6# 5 ; 1# '5 ; C# 5 ; ;# '5 ;#

'>

'F

o)ect

Lens

F

F

image


28/38


%. Sim*le amera * .he diagram elow shows the structure of a simple camera# In the o+es

pro"ided, write the names of the parts shown#

For each of the parts you ha"e named, state its function#

6ens? to focus a sharp image onto the film

1ilm? to record the image

iaphragm? to ad-ust the si+e of the aperture 3control the rightness of image4.

Shutter? to open and shut the camera so that the film is e5posed only for a short time.

&. Slide *ro;e!or * .he diagram elow shows the structure of a simple camera# In the o+es

pro"ided, write the names of the parts shown

Complete the ray diagram ao"e to e+plain how the slide pro)ector wor!s#

'?

;iaphragm

ad)ustment ring

Focusing

screw

Film drum

*ondenser *oncave

mirror

Light source

slide

Pro-ector

lens

creen

6ens

1ilm

Shutter

iaphragm


29/38


7. A#!ronomial !ele#o*e *

0a3in' of !-e a#!ronomial !ele#o*e.

• .he astronomical telescope consists of ' %on+er'in' di+er'in'& lenses#

•.he o)ecti"e lens has focal length, f o and the eye lens has focal length, f e where % f o 6 f e K f o 4 f e

• .he lenses are arranged such that the distance etween the o)ecti"e lens and the eye

lens is % f o


30/38


5. T-e om*o,nd miro#o*e *

S!r,!,re of !-e om*o,nd miro#o*e*

• 6 compound microscope consists of ' %con"erging K di"erging& lenses

•.he focal length of the eye lens is %long K short& and the focal length of the o)ecti"e lens is%long K short

• .he o)ecti"e lens is arranged such that the o)ect distance, u is %u f o < f o = u = # f o < u

#f o

• .he eye lens is used as a %magnifying K di"erging K pro)ector& lens#

• .he total length, s, etween oth lenses is % s f o @ f e @ s 9 f o@f e &

Complete the ray diagram ao"e to show how the compound microscope wor!s#

C-ara!eri#!i# of ima'e formed () om*o,nd miro#o*e*

• .he first image formed y the o)ecti"e lens is %realK"irtual @ diminishedKmagnified @

uprightKin"erted

• .he final image is %realK"irtual @ diminishedKmagnified @ uprightKin"erted

E$eri#e 1 9a2 * 6 compound microscope consists of two lenses of focal lengths ' cm and $0 cm#1etween them, which is more suitale as the eye lens 8+plain your answer#

The !" cm lens is used as the eye lens ecause it will ma:e a shorter microscope #

9(2* 2ow would you arrange the lenses in %a& to ma!e an astronomical telescope

Ase the !" cm lens as the o-ective lens and the # cm lens as the eye lens #

(0

/)ect

L0

Fe

Fo

Le 8ye

Image#


31/38


Reinforemen!*

Par! A*

$# 1etween the following statements aout reflection of light, which is no! true

6# 6ll light energy incident on a plane mirror is reflected#

1# .he angle of incidence is always the same as the angle of reflection#

C# .he incident ray, the reflected ray and the normal to the point of incidence, all lie on the

same plane#

;# .he speed of the reflected ray is the same as the speed of the incident ray#

'# 6 oy stands in front of a plane mirror# 2e oser"es the image of some letterings printed on his

shirt# .he letterings on his shirt is as shown in Figure $#

1etween the following images, which is the image oser"ed y the oy

(# Figure ' shows an o)ect, / placed in front of a plane mirror# 1etween the positions 6, 1, C and

;, which is the position of the image

4# 6 student is mo"ing with a "elocity of ' m s:$ towards a plane mirror# .he distance etween the

student and his image will mo"e towards each other at the rate

6# ' m s:$ 1# ( m s:$ C# 4 m s:$ ;# 5 m s:$ 8# = m s:$

5# .he tale elow shows the characteristics of the images formed y a conca"e mirror for "arious

positions of the o)ect# 6ll symols used ha"e the usual meanings# hich of them is no! !r,e

Figure $

6 1 C ;

/

6 1 C ;

Plane mirror

Figure '

($


32/38


Po#i!ion of o(;e! C-ara!eri#!i# of ima'e

6 u 9 #f ;iminished, in"erted, real

1 f = u = #f Magnified, in"erted, real

C u f ame siBe, in"erted, real

; u = f Maginfied, upright, "irtual

=# hich of the following ray diagram is correct

># .he depth of a swimming pool appears to e less than its actual depth# .he light phenomenon

which causes this is

6# 7eflection

1# 7efraction

C# ;iffraction

;# Interference

?# .he critical angle in glass is 4'o# hat is the refracti"e inde+ of glass

6# $#' 1# $#( C# $#4 ;# $#5 8# $#=

A# hich of the following are the characteristics of an image formed y a magnifying glass

6# Magnified, "irtual, in"erted

1# ;iminished, real, upright

C# Magnified, "irtual, upright

;# ;iminished, "irtual, in"erted

50o

50o

C F

Con"e+ mirror

C F

Conca"e mirror Plane mirror

6 1 C

('


33/38


$0# 6 student is gi"en three con"e+ lenses of focal lengths ' cm, $0 cm and 50 cm# 2e wishes to

construct a powerful astronomical telescope# hich of the following arrangements should he

choose

Focal length of o)ecti"e lens K cm Focal length of eye lens K cm

6 50 '

1 $0 $0

C ' 50

; 50 $0

Par! >

$#

Figure ( shows the eye of a person loo!ing at a fish#

a& !etch a ray diagram consisting of ' rays originating from the eye of the fish to show why the

image of the fish is seen closer to the surface#

& .he fish is at a depth of ' m# If the refracti"e inde+ of water is $#((, calculate the apparent

depth of the fish#

depthapparent

depthreal=n

depthapparent

'((#$ =

(pparent depth !.& m

air

water

8ye

Figure (

Image

((


34/38


'#

a& tarting with the lens formula, f vu

$$$=+ , deri"e an eEuation that gi"es the relationship

etween liner magnification, m and the image distance, v# 2ence s!etch the graph of m against v on

the a+es pro"ided elow#

f

v

v

v

u

v=+

f

vm =+$

$$

−= v f

m

%& tate the "alue of m at the point of intersection of the graph with the "ertical a+is#

:$

%c& ;escrie how you would determine the focal length of the lens using the graph#

The gradient of the graph gives the value of !


35/38


$#

6 student used a slide pro)ector to pro)ect a picture onto the screen# Figure $a and $ show the

relati"e positions of the slide, pro)ector lens and the screen#

It is oser"ed that when the screen is mo"ed further away %Figure $&, the lens of the pro)ector has

to e mo"ed nearer to the slide to otain a sharp image#

1ased on your oser"ations and !nowledge of lenses@

a& ma!e one suitale inference#

The image distance is dependent on the o-ect distance

& state an appropriate hypothesis that could e in"estigated#

The greater the o-ect distance, the smaller the image distance

c& descrie how you would design an e+periment to test your hypothesis using a con"e+ lens,

filament ul and other apparatus#

In your description, state clearly the following*

%i& aim of the e+periment

To investigate the relationship etween o-ect distance and image distance for a conve5 lens.

%ii& "ariales in the e+periment

lide

creen

image

Figure $a

Figure $

Pro)ector

lens

Pro)ector

lens

lide

creen

image

(5


36/38


Manipulated variable? o-ect distance.

Response variable? image distance.

Fixed variable? focal length of lens#

%iii&List of apparatus and materials

Apparatus? light ul, conve5 lens of focal length !" c , white screen, metre rule, low

voltage power supply and lens holder

%i"& 6rrangement of the apparatus

%"& .he procedure of the e+periment, which includes the method of controlling the manipulated

"ariale and the method of measuring the responding "ariale

Proed,re* $# 6rrange the apparatus as shown in the diagram ao"e#

'# 6d)ust the ul so that the o)ect distance %filament&, u is (5 cm from

the lens#

(# Light up the electric ul, ad)ust the screen position until a sharp image

of the filament is formed on the screen# 7ecord the image distance, v#

4# 7epeat steps ' and ( for o)ects distances of, u < (0cm, '5 cm, '0 cm,

and $5 cm#

%"i& .he way you taulate the data

/)ect distance,

u Kcm

Image distance,

v Kcm

(5#0

(0#0

'5#0

'0#0

$5#0

%"ii& .he way you would analyse the data

/)ect

distance

Image

distance

ullens

screen

Meter rule

Low "oltage power supply

Lens holder

(=


37/38


Plot the graph of v against u

'#

6 student carried out an e+periment to in"estigate the relationship etween o)ect distance, u,

and image distance, v, for a con"e+ lens# .he student used "arious "alues of u and recorded the

corresponding "alues of v# .he student then plotted the graph of uv against u @ v as shown in

Figure '#

Fig!re "

a& 1ased on the graph in Figure ',

(>

500

450

400

(5055

(000

'50

'000

$50

$00

50

uvK cm'

$0 '0 (0 40 50

u @ v K cm


38/38


%i& state the relationship etween uv and u @ v

----------------------------------

O! mar:

%ii& determine the "alue of u @ v when the "alue of uv < 400 cm'# how on the graph how

you otained the "alue of u "#

40 cm

From the "alue of u @ v otained, calculate the image distance, v when u < '0 cm#

#" @ v < 40

v < '0 cm

O$ mar:s

%iii& calculate the gradient of the graph# how clearly on the graph how you otained the

"alues needed for the calculation#

Bradient %""

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