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DELTA UNIVERSITY FOR SCIENCE AND TECHNOLOGY
FACULTY OF ORAL AND DENTAL MEDICINE
HANDOUT FOR
PRACTICAL PHYSICS II LAB
SPRING 2016
Prepared by physics group, All rights are reserved to the Faculty of Oral and Dental Medicine, Delta
University for Science and Technology.
1
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
2
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:
Fig (1.1): The focal length of a convex lens using 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 F 
100 100


f
3
1.2. General Method:
Fig (1.2): The general form of lens position
 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) =
4
2. Determination of the Focal Length and the Power of a
Diverging (Concave) Lens
fg
Fig (2.1): The group method for concave (diverging) 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.
fg (
1
2
3
Average
)
Mean value of the group focal length ( fg ) =
Power of the group of lenses Fg  
100 100


fg
5
Focal length of the converging lens (f1) =
Power of the converging lens F1  
100 100


f1
Power of diverging lens ( F2 ) = Fg - F1 =
Focal length of diverging lens  f 2  
100 100


F2
6
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) =
7
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).
8
 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) =
FL 
100 100 100 100




fg
f
The refractive index of the liquid (n) =
R 


n  1   FL
 1 
100 





100 
9
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:
10
 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
11
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 F m = 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
12
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
13
 A   min 
Sin

2


n
 A
Sin 
2
 Results:
Incidence
Angle
35
40
45
50
55
Deviation
Angle
A=
δmin =
n=
14
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:
H 
2NI
10r
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)
H  Ho  Tan( )
2NI
 Ho  Tan( )
10r
10rHo
I 
 Tan( )
2N
I  K  Tan( )

where K 
10rHo
2N
Using Ohm's law for this circuit which has the form:
I
V
R  Ro
Substitute in the above equation:
V
 K  Tan( )
R  Ro
or
Cot ( ) 
K
( R  Ro )
V
Which is a straight line relation between cot(θ) and (R), have the slope = K / V and
intersects the R-Axis at (Ro).
15
 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:
Recorded Deflections
R
θ1
θ2
θ3
θ4
Average (θ)
Cot(θ) =
1/Tan(θ)
16
Given Data
V = 3 Volt
Ho = 0.3 Orested
N = 50
G=
K = V · Slope =
r=
17
Experiment No. (06) Comparison between the Magnetic
Moments of Two Magnets using the Deflection Magnetometer
General Case


M1
d12  L12

M2
d 22  L22


2
2
d 2 tan 1
d1 tan  2
(1)
 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 (d 1) 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 (d 1) 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)
 M1
 M2
6. Calculate the ratio between the magnetic moments 

 using Eq (1).

7. Repeat all the above steps for three different distances for each magnet and find the
 M1
 M2
ratio 

 in each case and then calculate the average value.

18
 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:
19