Post office box Experiment for std 8 to 12 Physics

 POST OFFICE BOX

Aim:-

A post office box and other necessary instruments are given to you. Take three appropriate ratios of the resistances in the two arms of Post Office Box and determine the values of two unknown resistances.

Now connect the unknown resistances in series and parallel respectively and verify the laws of series and parallel combinations of resistances.

PRINCIPLE :- 

It works on the principle of balanced Wheatstone bridge.

APPARATUS :-

A Battery,

unknown resistance (Rx & Ry),

Post Office Box, 

a galvanometer, 

rheostat, 

connecting wires.

Post Office Box Apparatus

Condition 1 Resistance Rx connect between C and D

Post Box Wiring Diagram find Unknown Resistance Rx 

Condition 2 Resistance Ry connect between C and D

Post Box Wiring Diagram find Unknown Resistance Ry

Post OfficeBox line diagram Series connection Rx and Ry

Series connection of Rx and Ry wiring diagram

Parallel Connection line Diagram of Rx and Ry

Wiring Diagram Parallel connection of Rx and Ry

CALCULATIONS :-

Series connection, R’s = Rx + Ry + …..Ohm

Parallel connection, R’p = Rx Ry  /  Rx + Ry = ….Ohm.

RESULT :-

(1) Unknown resistance, Rx = ….Ohm. , Ry = ….Ohm

Observation for Post Office Box Experiment

Calculation table for Post Office Box

CONCLUSION :

The experimental and theoretical values of equivalent resistance for series and parallel connections are equal,within the experimental error. This implies the validity of the rules for the different combinations of resistances.

Precautions

 All plug keys of Post Office Box must be tight.

 Contact points of K1 and K2 must be cleaned  with sand paper.

 Galvanometer should be very sensitive.

 Throughout the experiment  press key K2(battery key) first and then key K1(galvanometer key).

More Video : Post Office Box Video presentation.

http://youtu.be/vG1Bkh1V7RY

Post Office Box Experiment.

Prepare Ammonia gas in Laboratory science 8 to 12

18 . To prepare ammonia gas in the laboratory and study its properties.

AIM : To prepare ammonia gas in the laboratory and study its properties

THEORY : On heating a mixture of ammonium chloride and calcium hydroxide, we get ammonium gas.

APPARATUS : Big hard glass tube, delivery tube, hollow glass tube, Bunsen burner, glass rod, two single-holed rubber cork, four to five gas jar with lids, stand and one CaO bottle as shown in the figure.

CHEMICALS : Calcium hydroxide, ammonium chloride, concentrated hydrochloric acid, red and blue litmus papers.

Prepare Ammonia Gas in Laboratory 

Observation
Colour of ammonia gas :
Odour or smell of ammonia gas :
Ammonia gas is collected by downhard displacement of air therefore it is than air.
Use moist red and blue litmus papers and check the effect on ammonia gas.

Conclude :
Wet red litmus :
Wet blue litmus :

Conclusion : What happens when a glass rod is dipped in concentrated HCL is brought near the mouth of gas jar containing ammonia ?

More details see Video.

Prepare Ammonia Gas in Laboratory Science practical animation video

Exothermic reaction for std 8 to 10

To measure the change in chemical reactions and conclude whether the reaction is exothermic or endothermic.

AIM : To measure the change in chemical reactions and conclude whether the reaction is exothermic or endothermic.

THEORY : During the chemical reaction if the temperature increases the reaction is exothermic and if temperature decreases the reaction is endothermic.

APPARATUS : Conical flask, 250 ml. Beaker, Stand, Thermometer, Glass rod, measuring cylinder, stirrer.

MATERIAL : Dilute hydrochloric acid, Zinc metal, Solid ammonium chloride,

Exothermic reaction

Observation : 

(1) initial temperature of dilute hydrochloric acid 0 C.
(2) Temperature of the mixture when Zinc metal dissolves in hydrochloric acid = 0 C.
(3) Difference of temperature = 0 C.
(4) Give chemical reaction of Zinc metal with hydrochloric acid.

NOTE :

 (1) Similarly heat of neutralization in neutralization reaction between dilute hydrochloric acid and sodium hydroxide can be measured.
(2) The increase in temperature can be noted when dissolution of solid sodium hydroxide in water is carried out.

PRACTICAL USES

The combustion reactions of kerosene, 

Petrol, 

LPG are exothermic, 

therefore these substance are used as fuel.

more Video presentation:

Exothermic reaction animation video

Focal Length by an Image of far distance object for std 8 to 10

To determine the focal length of a convex lens by obtaining an image of a far distance object. 

AIM : To determine the focal length of a convex lens by obtaining an  image of a far distance object.

PRINCIPLE :  Rays parallel to the axis, after being refracted by a convex lens, are focused on the principal focus. Distance   between the optical centre and the principal focus is known as the focal length.

APPARATUS   :   Convex lens, Stand, Screen, Foot-rule, etc,.

Focal length of a  far distance object

Observation : Distance between the optical center of the lens and the image on the screen = Focal length of the lens  f =   cm...         

Practical uses : Convex lens of proper focal length are used in optical instruments like simple microscope, compound microscope, telescope, etc,. Also the method given here in the simplest way to estimate the focal length of a convex lens.

Learning through Innovative technique picture

http://www.flickr.com//photos/physics_for_fun/show/with/5279683649/

To determine the focal length of a concave mirror by far away image.

2. To determine the focal length of a concave mirror by obtaining an image of a far distance object

AIM :- To determine the focal length of a concave mirror by obtaining an image of a far distance object.

APPARATUS  :- A concave  mirror of diameter approximately 10 cm., stand, screen, foot-rule, etc.

PRINCIPLE   :- Rays coming from a far distance object are almost parallel. Such rays, parallel to the principal axis, after being reflected by a concave mirror, are focused at the principal focus of the mirror. Distance between the principal focus and the pole of the mirror is known as the focal length.

NOTE  :  Here screen should be taken small, so that rays coming from the object are    not blocked by the screen itself. Diameter of the screen here can be   approximately 3 – 4 cm.

Focal Length of Concave mirror

Parallal rays of a Image 

Focal length of image on concave mirror

OBSERVATION

Distance between the pole of the mirror and the image on the screen = focal-length =                            CM.

CONCLUSION

PRACTICAL USES

Concave mirrors are used in head lights of vehicles, solar furnace, solar cooker, shaving mrror, etc. For all such applcatons it is necessary to know the focal length of the mirror to used. It can be estimated using the given method.

Video

To determine the focal length of a concave mirror by obtaining an image of a far distance object.

Focal length of concave mirror of a far away image.wmv

Angle of Incidence, Angle of image through Glass Slab experiments for std 8 to 12

To draw the path of a ray passing through a glass slab and, hence, to measure the angle of incidence and the angle of image.

AIM : To draw the path of a ray passing through a glass slab and, hence, to measure the angle of incidence and the angle of image.

PRINCIPLE :     When an oblique ray of light enters from one      transparent medium to another transparent medium,  at the surface separating these two media, the light  ray changes its path. This phenomenon is called  refraction of light. When a ray of light passes through  a glass-slab, it is refracted twice, as a result of which, the emergent ray becomes parallel to the incident ray.

APPARATUS :   Glass –slab, Drawing-board, Drawing paper (White),  Foot-rule, Pencil, Pins, Push pins and Protractor.

Paper fit with pins and set Glass Slab

Ø  Fix a white drawing-paper on the drawing board using push pins.  Now place the glass-slab on it and mark its position PQRS by drawing its out-line using a pencil.

Draw Ray AB not perpendicular to PQ

Ø  Now draw a ray AB such that it is not perpendicular to PQ. Fix two pins upright with separation of 2-3 cm on this ray.

See Image from another side and set P3 P4

Ø    Now try to see the images of P₁ and P₂ from side RS and fix pins P₃  and P₄ upright so that images of P₁ and P₂ and pins P₃ and P₄ become collinear at their lower ends.

Remove pins and Glass slab

Ø  Now remove the slab and the pins obtain emergent ray CD by drawing a line passing through marks of P₃ and P₄, which intersects RS at C.

Ø  Join  B and C to complete the path of the ray. Now draw a normal MN to the surface PQ in such a way that it passes through B. Also       draw M’N’, through C to the surface RS.

Measure Angle of Incidence and Angle of Emergence.

Ø  Measure ÐAMB (Angle of Incidence) and ÐOCN’ (Angle of Emergence).

By changing Angle of Incidence repeat the experiment

Ø  Repeat the experiment for various values of angle of incidence AMB and note your observations in the table.

Angle of Incidence Video

Angle of Incidence, Emergence, Refraction through glass slab.wmv