Electricity. Ohms law. and all other 10th standard physics concepts part 1. see other parts for more information.

1. SRV PUBLIC SCHOOLS, TIRUCHIRAPALLI
ONLINE CLASS FOR GRADE 10
SUBJECT : PHYSICS
TEACHER NAME : Mr. DANIELAMIRTHA RAJ
DATE : 29.04.2020

2. 12. ELECTRICITY
GRADE – X- SCIENCE - NCERT
Mr. A. Michael Rayar,
TGT, SRV Public School, Tiruchirapalli - 620009

3. SIMPLE CIRCUIT AND CURRENT FLOW

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

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

6. Connecting Ammeter and Voltmeter in a circuit
Ammeter
Series
Voltmeter
Parallel

7. Circuit Diagram
A Schematic diagram, in which different
components of the circuit are represented by
the symbols conveniently used.

8. Circuit symbols

9. Circuit symbols

10. Circuit symbols

11. Practice
Draw the schematic diagram of an
electric circuit consisting of a battery
of two cells of
1.5V each, three resistance of 5 ohm,
10 ohm and 15 ohm respectively and
a plug key all connected in series.

12. Ohm’s law
• Relates Potential difference and Current
Georg
Simon
Ohm

15. Kink

20. Things that
disturbs the
water flow
1.Presence of
kink
2.Pressure

21. Kink Resistor

22. Tank potential Battery potential

23. Comparing the flow of Electric current
in wire with the flow of water in hose.
•When pressure is high, the flow
of water is high and vice versa.
•When there is a presence of kink,
then the flow of water is low and
vice versa.

24. •Then, with respect to electric
current,
•When the potential difference is
high, the flow of current is high.
and vice versa.
•Then,
•𝑉 ∝ 𝐼

25. • When there is a presence of resistor,
then the current decreases and vice
versa.
• Then,
• 𝑅 ∝
1
𝐼
, 𝐼 =
1
𝑅
• Combining these two equations we
get,
• 𝐼 =
𝑉
𝑅
, 𝑜𝑟 𝑉 = 𝐼𝑅 Which we call it as
Ohm’s law.

26. Rheostat
The device used to regulate current without
changing the voltage source is called
variable resistance

29. Ohm’s law
The potential difference , V, across the ends
of a given metallic wire in an electric circuit is
directly proportional to the current, I, flowing
through it, provided the temperature is same
V I
V / I = Constant = Resistance (R)
V= I R

30. Ohm’s law

35. Problems
1.The potential difference required to pass a
current 0.2 A in a wire of resistance 20 ohm is
_________.
i)100 V ii) 4 V iii) 0.01 V iv) 40 V
Answer = ?

36. Question
• 2.How much current will an
electric bulb draw from a 220
v source. If the resistance of
the bulb filament is 1200
ohm?

37. Answer
• We are given
• V = 220V;
• R=1200 ohm.
• From equation I=V/R
• I=220 V/1200 ohm = 0.18 A

38. Question
3.How much current will an
electric heater coil draw
from a 220 V source, if the
resistance of the heater coil
is 100 ohm?

39. Answer
We are given,
V=220 V, R=100 ohm.
From the equation I=V/R
I=220V /100 ohm = 2.2A.
Note : The difference of current drawn by
an electric bulb and electric heater from
the same 220V source!

40. Question
4. The potential difference
between the terminals of an
electric heater is 60 V when it
draws a current of 4 A from the
source. What current will the
heater draw if the potential
difference is increased to 120V?

41. Answer
We are given, potential difference V=60V, Current I=4A.
According to Ohm’s law,
R=V/I
=60V / 4A
=15ohm.
When the potential difference is increased by 120V, the
current is given by,
Current = V/R
=120V / 15 ohm
=8A.
The current through the heater becomes 8A.

42. Current and Resistance relation
Current is inversely proportional to
Resistance
Think:
If the resistance is doubled, the Current will
be halved.

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

44. FACTORS ON WHICH RESISTANCE DEPENDS ON

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

46. Factors on Which Resistance depends on
Depends on Length

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

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

49. 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

52. 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

53. Resistivity of materials

54. Problems
• Q1,Resistance of a metal
wire of length 1m is 26 ohm.
If the diameter of the wire is
0.3mm, what will be the
resistivity of the metal at the
temperature?

55. Answer
We are given the resistance R of the wire =
26ohm, the diameter d=0.3mm = 3x10-4m.and
the length l of the wire = 1m.
Therefore the resistivity of the given metallic
wire is
𝜌 =
𝑅𝐴
𝑙
= R𝜋𝑑2
/4𝑙
Substituting the values in this gives
𝜌=1.84x10-6 Ohm m
The resistivity of the metal at is 1084x10-6 ohm
m.

56. 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?

57. 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.

58. 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?

59. Answer
When the length of the wire is doubled, still its
volume remains constant.
Volume before stretching = A1l1
Volume after stretching =A2l2
Since volume is constant
A1 l1 = A2 l2
Given l2 = 2l1
Therefore,
A1 l1=A2 x 2l1
A1=2A2
A2=A1 / 2

60. 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 2l2/(A1/2) = 4 𝜌 l2/A1
RI = 4x2 R
RI = 8R.

61. 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.

62. 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.

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

64. 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