1

DELTA UNIVERSITY FOR SCIENCE AND TECHNOLOGY

FACULTY OF ORAL AND DENTAL MEDICINE

Prepared by physics group, All rights are reserved to the Faculty of Oral and Dental Medicine, Delta

University for Science and Technology.

HANDOUT FOR

PRACTICAL PHYSICS II LAB

SPRING 2016

2

Contents

Experiment No. (01) Power of Spherical Lenses ---------------------------------------------------------------- 3

1. Determination of the Focal Length and the Power of a Converging (Convex) Lens ------------------------- 3

1.1. Coincidence Method: -------------------------------------------------------------------------------------------- 3

1.2. General Method: ------------------------------------------------------------------------------------------------- 4

2. Determination of the Focal Length and the Power of a Diverging (Concave) Lens ------------------------- 5

Experiment No. (02) Determination of the Refractive Index of a Liquid using Liquid Lenses ------------- 7

1. Using concave mirror ------------------------------------------------------------------------------------------------ 7

2. Using Convex Lens and Plane Mirror ------------------------------------------------------------------------------ 8

Experiment No. (03) Power of Spherical Mirrors ------------------------------------------------------------- 10

1.Determination of the power and the focal length of concave mirror: 10

1.1. Coincidence Method: ------------------------------------------------------------------------------------------- 10

1.2. General Method: ------------------------------------------------------------------------------------------------ 10

2. Determination of the power and the focal length of Convex mirror: --------------------------------------- 12

Group Method: ------------------------------------------------------------------------------------------------------- 12

Experiment No. (04) The Prism --------------------------------------------------------------------------------- 13

Experiment No. (05) Verification of ohm's law by tangent galvanometer ---------------------------------- 15

Experiment No. (06) Comparison between the Magnetic Moments of Two Magnets using the Deflection

Magnetometer ---------------------------------------------------------------------------------------------------- 18

3

Experiment No. (01) Power of Spherical Lenses

1. Determination of the Focal Length and the Power of a Converging

(Convex) Lens

1.1. Coincidence Method:

Method

1. Keep a light source (O) (illuminated arrow) at a distance from the lens and keep a

plane mirror behind the lens such that the mirror surface is perpendicular to the lens

axis.

2. Adjust the position of the lens until a sharp image (I) is formed on the surface

contains the source (O).

3. Record the distance between the lens and the light source (O). This distance

measures the focal length (f) of the lens.

4. Repeat the steps (2 and 3) many times and calculate the average value of the

distances, which must be nearly equal.

Results

No. 1 2 3 Average

f ( )

Main value of the focal length of the lens ( f ) =

Power of the lens 100100

fF

Fig (1.1): The focal length of a convex lens using coincidence method

4

1.2. General Method:

Method

1. Put the lens on its holder and keep the distance of an illuminated arrow (O) from the

lens greater than the approximate focal length of the lens.

2. Looking from the other side of the lens adjust the position of a screen until a sharp

image of the used arrow (I) is formed on the screen.

3. Record the readings on the optical bench meter scale corresponding to the positions

of (O) and (I) from the lens, (x) and (y), respectively

4. Repeat for different observations (not less than five).

5. Complete the table and find F=(X+Y).

Results

No. x y X ( ) Y ( ) F = X + Y

1

2

3

4

5

Average power of convex lens (Fav) =

Fig (1.2): The general form of lens position

5

2. Determination of the Focal Length and the Power of a

Diverging (Concave) Lens

Method

1. Put the converging lens in contact with the diverging lens on a holder in front of

the source of light (O) in such away that the convex lens is facing the light source.

2. Put a plane mirror on a holder behind the group of lenses. Move the holder of the

two lenses until a sharp image is formed on the source surface, as in Fig (2.1).

3. Measure the distance between the source and the middle of the holder of the

lenses. This distance equals the focal length of the group of lenses (fg).

4. Repeat these steps many times. Calculate the average of the group focal length.

5. Calculate the power of the group (Fg).

6. Find the focal length of the converging (convex) lens by any method say it is (f1 cm).

Then calculate its power (F1).

7. Determine the power of the diverging lens (F2).

Results

No. 1 2 3 Average

fg ( )

Mean value of the group focal length ( fg ) =

Power of the group of lenses 100100

g

gf

F

fg

Fig (2.1): The group method for concave (diverging) lens

6

Focal length of the converging lens (f1) =

Power of the converging lens 100100

1

1f

F

Power of diverging lens ( F2 ) = Fg - F1 =

Focal length of diverging lens 100100

2

2F

f

7

Experiment No. (02) Determination of the Refractive Index of a

Liquid using Liquid Lenses

1. Using concave mirror

Method

1. Place the concave mirror horizontally on the wooden block.

2. With the help of the optical needle, remove the parallax between the needle and its

image. This position of the tip of the needle corresponds to the centre of curvature

of the mirror. Measure the distance (PC = r).

3. Now pour a little quantity of the liquid on the mirror and again remove the

parallax between the needle and its image. Measure the distance (PC' = r').

4. Repeat the observations many times.

Results

No. PC = r ( ) PC' = r' ( ) n = PC/PC' = r/r'

1

2

3

Average

Refractive index of the liquid (n) =

8

2. Using Convex Lens and Plane Mirror

Method

1. Place a plane mirror on the stand and a convex lens over it.

2. Put a solid arrow in the clamp of the stand and move it till an inverted image is

formed. Now remove the parallax between the arrow and its image.

3. Measure the average of the distance of the arrow from the plane mirror and from

the upper surface of the lens. This gives the focal length of the convex lens (f).

4. Repeat this several times and find out the mean value of (f).

5. Now place a few drops of the given liquid in between the lens and the mirror. So

that, a thin plane-concave lens of the liquid is formed.

6. Now adjust the arrow along the vertical stand till its inverted image formed by the

combination coincides with the arrow i.e., when no parallax exists

7. Measure the average of the distance of the arrow from the plane mirror and from

the upper surface of the lens, which is the focal length (fg) of the combination.

8. Repeat the three steps many times and find out the mean value of (fg).

9. Calculate the refractive index (n).

9

Results

No. f ( ) fg ( )

1

2

3

Average

Mean of focal length of convex lens (f) =

Mean of focal length of group lens (fg) =

The power of the liquid lens (FL) =

100100100100

ffF

g

L

The refractive index of the liquid (n) =

1001

1001

RFn L

10

Experiment No. (03) Power of Spherical Mirrors

1. Determination of the power and the focal length of concave mirror:

1.1. Coincidence Method:

Method:

1. Put the mirror in front of the source and move it until you get sharp image.

2. Measure the distance from the mirror to the illuminated object, which is the radius

of curvature (r).

3. Repeat the Last steps many times and take the average of (r).

Results:

No. 1 2 3 Average

R

Mean value of the radius (r) = … Cm

Focal length (f = r / 2) = ….. Cm

Power of the mirror (F) = …… Diopter

1.2. General Method:

11

Method:

1. Put the mirror at a distance greater than its focal length. then move a screen

between the mirror and the illuminated object until you get sharp image.

2. Record the distance from the illuminated object to the mirror is (x) and the

distance from the screen to the mirror is (y). then calculate X, Y and F=X+Y

3. Repeat the above steps for different values of (x)

4. Plot a relation between X, Y and then calculate the power from the intersections

of the straight line.

Results:

Observation x y X Y F=X+Y

1

2

3

4

5

Average power from the table (Fav) = … Diopter

12

2. Determination of the power and the focal length of Convex mirror:

Group Method:

Determination of the Group radius Determination of the lens' power

Method:

1. Find the focal length (fL) of the convex lens by any method. then calculate the

power of the convex lens FL = 100 / fL

2. Place the convex lens with the convex mirror on the same holder, and move the

group until you get sharp image.

3. Record the distance from the group to the illuminated object as (rg).

4. from (rg) calculate the focal length of the group (fg) then Fg = 100 / fg

5. Calculate the power of the convex mirror by Fm = Fg – 2·FL which is a negative

value.

Results:

Observation 1 2 3 Average

rg

Mean value for (rg) = … Cm

Focal length of the group (fg) = rg / 2

Power of the group (Fg = 100 / fg) = … Diopter

Focal length of the convex lens (fL) = … Cm

Power of the convex lens (FL) = 100/fL = …. Diopter

Power of the convex mirror (Fm) = Fg – 2·FL = … Diopter

13

Experiment No. (04) The Prism

Method:

[A] Determination of the apex angle(A):

1. Put the prism with its triangular base on the paper and draw the prism.

2. Draw two parallel lines with the apex in the center of the distance between them

as in the figure.

3. Put two pins on the line ED and look in the same face to find the reflected image

of the pins. then put another two pins inline with the images of the pins.

4. Remove the pins and draw a line connecting the positions of the pins to obtain

the direction of the reflected ray.

5. Repeat the same on the other face of the prism.

6. The angle between the two reflected rays is (2A) from which we determine the

Apex angle (A).

[B] Determination of the minimum deviation angle (δmin):

1. Put the prism on its triangular face and draw it on the paper.

2. Draw HD to represent the incidence ray with incidence angle (i) with the normal

to the face.

3. Put two pins on the Line HD and look for the image of the two pins in the opposite

face, then put another two pins inline with the pins images.

4. Draw EF by connecting the positions of the two pins to represent the refracted

beam.

5. Record the angle of deviation which is the angle between the incidence and

refracted beam.

6. Repeat all the steps with different incidence angles to obtain the corresponding

deviation angle.

7. Draw a relation between the incidence and deviation angles and determine the

minimum deviation angle δmin from the graph as shown in the figure

8. by Using the value of the Apex angle (A) and (δmin) calculate the refractive index

(n) from the relation

14

2

2

min

ASin

ASin

n

Results:

Incidence

Angle 35 40 45 50 55

Deviation

Angle

A =

δmin =

n =

15

Experiment No. (05) Verification of ohm's law by tangent

galvanometer

Theory:

Ohm's Law: "Voltage is directly proportional to the current for constant temperature."

For the tangent Galvanometer:

The magnetic field (H) formed due to a current ( I ) passing in the coil is given by:

r

NIH

10

2

The pointer deflects by angle (θ), which is because of two perpendicular fields:

1) The magnetic field produced by the coil (H).

2) The horizontal component of earth's magnetic field (Ho).

And the relation is given by: H=Ho · Tan(θ)

N

rHoK

TanKI

TanN

rHoI

TanHor

NI

TanHoH

2

10 where

)(

)(2

10

)(10

2

)(

Using Ohm's law for this circuit which has the form:

RoR

VI

Substitute in the above equation:

)()(

)(

RoRV

KCot

or

TanKRoR

V

Which is a straight line relation between cot(θ) and (R), have the slope = K / V and

intersects the R-Axis at (Ro).

16

Method:

1. Connect the circuit as shown.

2. Adjust the galvanometer at the meridian position. Where the pointer is

perpendicular to the coil.

3. Set the resistance to (R=10) from the resistance box.

4. Turn on the circuit.

5. record the deflections of the pointers θ1 and θ2

6. Reverse the current.

7. record the deflections θ3 and θ4

8. Calculate the average deflection θ = (θ1 + θ2 + θ3 + θ4)/4 and calculate Cot(θ)

9. Repeat the steps [5] to [8] with different values for (R).

10. Plot a relation between Cot(θ) and (R), Which is a straight line relation having

the slope = K / V and intersects the R-Axis at (Ro).

11. From the intersection with R-Axis determine Ro

From the Slope determine the radius of the coil (r).

12. To determine the unknown resistance (Rx), connect it instead of the resistance

box and repeat the steps [5] to [8]. To obtain Cot(θ) for the unknown resistance

and from the graph we determine (Rx)

Results:

R Recorded Deflections

Average (θ) Cot(θ) =

1/Tan(θ) θ1 θ2 θ3 θ4

17

G =

K = V · Slope =

r=

Given Data

V = 3 Volt

Ho = 0.3 Orested

N = 50

18

Experiment No. (06) Comparison between the Magnetic

Moments of Two Magnets using the Deflection Magnetometer

General Case

)1(tan

tan

2

1

1

2

22

2

2

2

22

1

2

1

2

1

d

d

Ld

Ld

M

M

Method

1. Put the magnetometer in Gauss first position, so that the two ends of the pointer are

at the zero readings of the scale.

2. Put the first magnet (L1) on one arm at the magnetometers parallel to its scale at a

distance (d1) between the middle of the magnet and the magnetometer center then

read of the deflections (θ11 and θ12).

3. Put the same magnet on the same arm at the same distance (d1) and chancing the

poles of the magnet and read the deflections (θ13 and θ14).

4. Repeat the steps (2) and (3) for the same magnet at the same distance (d1) on the

second arm of the magnetometer and find the deflections (θ15 and θ16) and s (θ17 and

θ18), then calculate the average deflection of the eight readings (θ1).

5. Repeat the steps (2-4) for the second magnet (M2) at different distance (d2) and find

the average deflection of the eight readings (θ2)

6. Calculate the ratio between the magnetic moments

2

1

M

M using Eq (1).

7. Repeat all the above steps for three different distances for each magnet and find the

ratio

2

1

M

M in each case and then calculate the average value.

19

Results Table (1): For the first magnet

Table (2): For the second magnet

Table (3): Form Tables (1) and (2) we can write the final results as: