Section 14.2 Where Charges Come From?

8/14/2019 Section 14.2 Where Charges Come From?

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Manhattan Press (H.K.) Ltd. 1

Section 14.2Section 14.2

Where charges come from?Where charges come from?

Section 14.2Section 14.2

Where charges come from?Where charges come from?

Conservation of chargeConservation of charge

Charge in atomCharge in atom


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Charge in atom

+

+

++

--

-

-

All substances are made up ofatoms

14.2 Where charges come from? (SB p. 6)

atom

nucleus

electrons negative charge

protons positive charge

neutrons - neutral


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Class Practice 1:Class Practice 1:Fill in the blanks with correct terms: electrons, neutrons,

nucleus, proton

Ans

wer

nucleus

proton

neutron

electron



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Charge in atom

-

-

-

-++

++

1 proton: 1.6

10

19

C

1 neutron: 0 C

1 electron: 1.6 1019 C

charge is negative

Unit of charge : coulomb(C)



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Charge in atom

Normally in atoms,

no. ofprotons= no. ofelectrons

no net charge

electrically neutral

Thinking 2Thinking 2


+

+

++

--

-

-

amount of+ve charges= amount of-ve charges


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-

electron lost

-

proton 4 (1.6 1019 C)

electron 3 (1.6 1019C)

net charge +1.6 1019 C

charges

positively charged

+ve charge > -ve charge


Losing an electron


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-

-

electron gained

proton 4 (1.6 1019 C)

electron 5 (1.6 1019C)

net charge 1.6 1019 C

charges

+ve charge < -ve charge

negatively charged


Gaining an electron


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neutral object

charging process

transfer of electrons

-

-

-

-

++++



Charge in atom

charged

discharged

-

- charged objectneutral object

charged object


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-

-

-

-++++

-

-

-

-

++++

-

transfer

of electron

Conservation of charge

total electric charges in isolated system

constant

Go to

Activity 2Activity 2



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To section 14.3
http://e-ch14_03.ppt/http://e-ch14_03.ppt/


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State one similarity and one difference of

the charges of an electron and a proton.

AnswerEqual in magnitude but opposite in sign.

Return to

TextText



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Inside an atom, negative electrons are

circulating around the positive nucleus.

What are the forces between them? Answer

Attractive electrostatic forces exist between

them.

Return to

TextText



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Lets start:

1. Place a green plastic transparent sheetabove a red one. Cut the sheets in the

same shape.

What is the colour of the combinedsheets?

Activity 2Activity 2

Analogue of charges in atomAnalogue of charges in atom

BlackAns

wer



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2. Consider the combined sheets to be an

atom. Let the red sheet carries positivecharges and the green sheet carries

negative charges in the atom.

What can be deduced from step 1?

Activity 2 (Cont)Activity 2 (Cont)


Inside an atom, there is an equal amountof positive and negative charges.

Therefore, an atom is neutral.

Ans

wer



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3. Now slowly shift the green sheet to the

right slightly.(a) What is the relation between the size

of the red colour part on the left and that

of the green colour part on the right?



Red colour is seen on the left with an

equal proportion of the green colour on

the right.

Ans

wer



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(b) What can be deduced from (a)? Is theatom charged?



When one side of an atom has more

negative charges, the other side should

have an equal amount of positivecharges. The atom does not carry net

charge overall and it is neutral.

Ans

wer



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4. Now cut a small piece from the green

sheet. If an atom loses negative

charges, what charges does it carry?



It carries net positive charges. Answer



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5. State any discrepancy between the

plastic sheets model and a real atom.



In a real atom, the positive charges areconcentrated at the centre rather than

distributed over the atom. The electrons

carrying negative charges are orbitingaround the positive charges.

Answer

Return to

TextText


Section 14.2 Where Charges Come From?

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