Resistors in series and parallel. For more other electricity chapters see our other files. Electricity 10th standard science - physics.

1. SRV PUBLIC SCHOOLS, TIRUCHIRAPALLI
ONLINE CLASS FOR GRADE 10
SUBJECT : PHYSICS
TEACHER NAME :Mr. DANIELAMIRTHA RAJ
DATE : 4.05.2020

2. 12. ELECTRICITY
GRADE – X- SCIENCE - NCERT

3. RECAP
Electric
Circuit
Charges
Q = ne ampere
Charge
Time
Electric
current
Electric
potential
Workdone
Charge
volt

4. RECAP
Current
Ammeter
Series Parallel
Voltmeter
Potential
difference
Circuit
diagram
Circuit
symbols
?

5. RECAP
Ohm’s law
Relates V
and I
!
Unit : Ohm
Resistance ‘R’ Depend
Length
Area of cross
section
Type of
material
Temperature

6. Resistance (R)
Property of conductor to resist the flow of charges
through it.
S.I unit of Resistance = ohm (Ω)
R = V / I
ohm

7. FACTORS ON WHICH RESISTANCE DEPENDS ON

8. Factors on Which Resistance depends on
Nichrome wire is connected

9. Factors on Which Resistance depends on
Depends on Length

10. Factors on Which Resistance depends on
Depend on Area of cross section

11. Factors on Which Resistance depends on
Depends on Type of material
Nichrome wire is connected

12. RESISTANCE DEPENDS ON
1.Length of the conductor
2.Area of cross section of the conductor
3.Nature of material of the conductor
4.Temperature of material of the
conductor

13. Resistance and Resistivity
Resistivity is also called as Specific Resistance

15. Bunch of tomatoes

16. 1 kg of tomatoes

17. RESISTANCE , RESISTIVITY Vs Temperature
Both Resistance and Resistivity of the
material depend on Temperature
Resistance of all pure metals increases
with increase in temperature
 But the resistance of alloys such as
Manganin, Nichrome is almost
unaffected by temperature

18. Resistivity of materials

19. RESISTANCE , RESISTIVITY Vs Temperature
Both Resistance (R) and Resistivity (ρ) of
the material depend on Temperature
Resistance of all pure metals increases with
increase in temperature
 But the resistance of alloys such as
Manganin, Nichrome is almost unaffected by
temperature
Insulators decrease their resistance with
increase in temperature

20. Resistivity of materials

21. Problems
• Q1,Resistance of a metal
wire of length 1m is 100 ohm.
If the diameter of the wire is
0.2mm, what will be the
resistivity of the metal at the
temperature?

22. Answer
L=1m ; R=100 ohm ; d=0.2mm
𝜌 =
𝑅𝐴
𝑙
=
𝑅
𝑙
𝜋r2 (Since r=d/2)
= R x 𝜋d2/4
=100x3.14x(0.2x10-3)2 /4
=100x3.14x0.04x10-6/4
=3.14x4x10-6/4
𝜌 =3.14x10-6 ohm m

23. Question
A wire of given material having
length l and area of cross section
A has a resistance of 4 ohm.
What would be the resistance of
another wire of the same material
having length l/2 and area of
cross section 2A?

24. Answer
For first wire,
R1 = 𝜌 l/A= 4ohm
Now for second wire,
R2 =𝜌(l/2)/2A= ¼ 𝜌 l/A.
R2 = ¼ R1
R2 = 1ohm.
The resistance of the new wire is 1 ohm.

25. Question
A wire of resistance 2 ohm
is stretched to double its
length. What is the new
resistance of the wire?
What is the change in
resistivity of the wire?

26. Answer
When the length of the wire is
doubled, still its volume remains
constant.
Volume before stretching = A1 l1
Volume after stretching =A2l2
Since volume is constant

27. A1 l1 = A2 l2
Given l2 = 2l1
Therefore,
A1 l1=A2 x 2l1
A1=2A2
A2=A1 / 2

28. So, when the length is doubled, the
area of cross section is reduced by
½.
So the new resistance would be
RI = 𝜌l2/A2 = 𝜌 2l1/(A1/2) = 4 𝜌 l1/A1RI
=4 R
=4 x 2 ohm
RI = 8ohm.

29. Question
The electric resistance of a certain wire of iron is R. If
its length and radius are both double, then
a) The resistance will be doubled and the specific
resistance will be halved.
b) The resistance will be halved and the specific
resistance will remain unchanged.
c) The resistance will be halved and the specific
resistance will be doubled.
d) The resistance and the specific resistance will
both remain unchanged.

30. Answer
𝜌=RA/l
=R1 𝛱r2/l
=R2 𝛱(2r)2
=2𝛱r2 xR2/l
R1 𝛱r2/l = 2R2 𝛱r2/l
R1=2R2
R2=R1/2.

31. Question
Two wires of same material
and same length have
radius r and 2r respectively.
Compare their resistance.

32. Answer
If R1 and R2 are the resistance
of two wires.
𝜌 =RA/l = R1 𝛱𝑟12/l = R2 𝛱𝑟22/l
R1/R2 = r22/r12 = (2r)2/r2
R2 = R1/4

33. PROBLEM - 2

35. COMBINATION OF RESISTORS
 Symbol of resistor
 Series connection
 Parallel connection

36. RESISTORS IN SERIES

37. Resistors in serius

38. RESISTORS IN SERIES
‘I’ is constant
‘V’ varies

39. RESISTORS IN SERIES
‘I’ is constant
‘V’ varies

40. RESISTORS IN SERIES
When several resistors are joined in series,
the resistance of the combination is always
equal to the sum of their individual
resistances
Effective resistance is always greater than
any individual resistance

41. RESISTORS IN SERIES

42. Question
A, what will be current in ammeter?
B, what will be voltage across 12 ohm resistor?
V
A
5V
5ohm 12ohm8ohm

43. Answer
A,
All resistors are connected in series. So,
Effective resistance Rs = R1 +R2 +R3
Rs= 5+8+12
=25ohm
By applying ohms law
V=IR
I=V/R (V=5V; R=25ohm)
I=5/25
I=1/5 A

44. B,
Voltage across 12 ohm resistor will be,
Since the same current flows through all
resistors and it was found to be 5A in
ammeter.
Again apply ohms law V=IR
V=1/5 x 12
=12/5
V across 12 ohm resistor =2.4V

45. Resistors in parallel

47. THANK YOU