section 14.3 different charging methods

8/14/2019 Section 14.3 Different Charging Methods

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Manhattan Press (H.K.) Ltd. 1

Section 14.3Section 14.3

Different charging methodsDifferent charging methods

Section 14.3Section 14.3

Different charging methodsDifferent charging methods

Charging insulator by rubbingCharging insulator by rubbing

Charging conductor by sharingCharging conductor by sharing Charging conductor by inductionCharging conductor by induction


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Conductors Insulators

copper

aluminium

iron

glass

plastic

air

Conductor and insulator

Go to

Activity 3Activity 3

Materials can be classified as:

14.3 Different charging methods (SB p. 11)


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Conductors

+

+

+

+ + +

+ + +

+ + +

- -- - - -

- -- - - -

- --

-

--

-

-

-

loosely held electrons

charges move easily from

one place to another

can conduct electricity


Conductor


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charges cannotmove easily

Insulators

+

+

+

+ + +

+ + +

+ + +

-

-

-

-

-

- -

-

-

-

-

-

electrons held

tightly by nuclei


cannot conduct electricity

Insulator


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Rubbing a polythene rod

with a neutral dry cloth

Charging insulator by rubbing

neutraldry cloth

polythene

rod

polythene

rod


electrons

Friction provides energy

to electrons to transfer


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Rubbing an acetate rod

with a neutral dry cloth


acetate

rod


electrons


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insulators can be charged by rubbing

neutral

dry cloth

polythene

rod


direction of flow ofelectrons depends onmaterials

charges reallocated no charges created / destroyed


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Class Practice 2:Class Practice 2:

1.Two plastic strips repel as shown.(a) How can you obtain the result

shown in the figure?

You are given two neutralplastic strips.

Ans

wer

Pull three fingers down the pair of

plastic strips, with one finger between them.



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Class Practice 2: (Cont)Class Practice 2: (Cont)

(b) Explain briefly the phenomenon in terms of the

charges on the strips.

Ans

wer

They repel each other

because they carry like charges.

rubbed

by

fingers



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2. Fig. (a) Fig. (b)

(a) How can you obtain the results

shown in Fig. (a) and Fig. (b)?


You are given two neutral

plastic balloons, which aremade of the same material.

You are given two neutral

plastic balloons, which are

made ofdifferent material.

Ans

wer


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In Fig. (a), rub the balloons with a piece of

woollen cloth.

In Fig. (b), rub the balloons againsteach other.


Fig. (a)

Fig. (b)



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In Fig. (a), they repel each other

because they carry like charges.

In Fig. (b), they attract each other

because they carry unlike charges.


(b) Explain briefly the phenomenashown in Fig. (a) and Fig. (b)

in terms of the charges

on the balloons. Ans

wer


Fig. (a)

Fig. (b)


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Charging conductor by sharing

insulated

stand

metal

sphere

insulated

conducting rod


electron

sphere

carries -ve

charges


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conductor

less charges more charges

Uneven sharing of charges


electrons


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Van de Graaff generator

foam board

Van de

Graaff

generator


for generating charges



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Van de Graaff

generator

The hairscarry like

charges &

stand on their

ends!-

-

--

-- - -

-

-

-

-------

--

- ---

---

--

-

- --

--

roller

plasticconveyor

belt

charged by

rubbing

metaldome


Thinking 4Thinking 4



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symbol

Earthing

Earthingcharge sharing between abody & the earth



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Earthing

size of earth >> size of sphere

electrons go to sphere / earth

sphere becomes electrically neutral


electrons electrons


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Charging conductor by induction

electrons flow

from earthmetal

sphere

insulated positivelycharged metal rod


+ve charges on rod

attract ve charges

on sphere


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-ve charges

are not free

to move

____

_

___

__

sphere

carries -ve

charges

Charging conductor by induction




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Example 1:Example 1:A metal-coated ball hanging on a nylon string is brought near a

negatively charged dome of a Van de Graaff generator asshown. Describe briefly what happens to the ball.

Solut

ion



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Example 1: (Cont)Example 1: (Cont)


The ball is attracted towards the dome at first. This is due to the attraction

between the negative charges on the dome and the positive charges

induced on the left hand side of the ball (Fig. (b)). But when the ball

touches the dome, it shares the negative charges with the dome. The dome

and the ball then carry like charges and the ball is repelled (Fig. (c)).

Fig. (b) Fig. (c)


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Class Practice 3:Class Practice 3:1.Two insulated spheresA and B are in contact as shown.

You are given a positively charged rod. How do youcharge sphereA positively and sphere B negatively by

induction after both of them are separated? Explain

briefly with the help of two diagrams.

Ans

wer



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Bring the positively charged rod

near sphere B. Negative and positive charges

are induced onspheres B and A respectively.

Fig. (a)

Separate the spheres and then take awaythe rod. Now, sphere A carries positive charges

and sphere B carries negative charges.

Fig. (b)


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Class Practice 3: (Cont)Class Practice 3: (Cont)2.The figure shows an insulated neutral metal sphere. How

do you charge it positively by(a) a positively charged rod, and

(b) a negatively charged rod?

Explain briefly.

(a) By sharing: Touch the sphere with the

positively charged rod.

Ans

wer

(b) By induction: Place the negatively

charged rod near the sphere. Touch the sphere momentarily

with a finger.Then take away the rod.



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To section 14.4
http://e-ch14_04.ppt/http://e-ch14_04.ppt/


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Charging methodsCharging methods (A) Rubbing(A) Rubbing

Lets start:

1. Cut a piece of newspaper into very small

pieces and put them on a table.

2. Bring a plastic ruler close to the paper

pieces (Fig. (a)).

What happens? Answer

There is no observable change.


Fig. (a)


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Activity 3 (Cont)Activity 3 (Cont)


3. Then rub the plastic ruler many times

with a woollen cloth.

4. Bring the ruler close to the paper pieces

again. What happens?

The paper pieces are attracted by

the ruler.


Ans

wer


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5. Try rubbing a metal ruler with a woollen

cloth. Then, bring it close to the paper

pieces. What happens?

6. Which kind of materials, metal or plastic,

can attract the paper pieces afterrubbing?

Answer

Plastic.

There is no observable change.

Ans

wer



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Lets start:

1. Ask your classmate to

stand on a foam board.

2. Ask him to touch the metaldome of a Van de Graaff

generator with his hand

(Fig. (b)).3. Turn on the generator.


Charging methodsCharging methods (B) Sharing(B) Sharing


Fig. (b)

iff h i h d ( )


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4. What happens to your classmates

hairs?

5. Explain briefly the result in step 4.


Charging methodsCharging methods (B) Sharing(B) Sharing

The hairs stand on their ends.

The charges on the metal dome flow to

his body through his hand. Therefore, his

hairs carry like charges and repel each

other. This makes the hairs stand on their

ends.

Answe

r

Answe

r

Return to

TextText


14 3 Diff h i h d (SB 15)


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Refer to Fig. 14.8, what is the useof the foam board under the

student? If the board is taken

away, what happens to thestudent?

Ans

wer

The foam board is used to isolate

the body from the ground. If it is

taken away, charges flow throughthe student to the ground.

Therefore, he will get an

electric shock!Return to

TextText

foam board

Van deGraaff

generator


14 3 Diff t h i th d (SB 17)


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In Fig. 14.12(b), if the finger touches the

sphere without the presence of the charged

rod, can the sphere be charged?

Ans

werNo. If the sphere is touched

without the presence of the rod,

all the positive and negative

charges on the sphere will

recombine.Return to

TextText


section 14.3 different charging methods

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