Resistance and factors affecting It! Episode 3
Transcript of Resistance and factors affecting It! Episode 3
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Resistance and factors affecting It!Episode 3
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ELE
CTR
ICIT
Y Electric Current & Potential Difference
Resistance & Factors Affecting it
Ohm’s Law
Heating effects of Electric Current
Resistance in Series
Resistance in Parallel
Electrical Power & Energy
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ELE
CTR
ICIT
Y Electric Current & Potential Difference
Resistance & Factors Affecting it
Ohm’s Law
Heating effects of Electric Current
Resistance in Series
Resistance in Parallel
Electrical Power & Energy
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V = IRV = I/R
V = W/Q I = R/V
A B
C D
Q1. Which formula represents Ohm’s law?
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V = IRV = I/R
V = W/Q I = R/V
A B
C D
Q1. Which formula represents Ohm’s law?
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200 V 100 V
250 V 50 A
A B
C D
Q2. Calculate the potential difference between two points of a terminal, if an electric current of 10 A is flowing through it having resistance of 20Ω.
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Q2. Calculate the potential difference between two points of a terminal, if an electric current of 10 A is flowing through it having resistance of 20Ω.
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200 V 100 V
250 V 50 A
A B
C D
Q2. Calculate the potential difference between two points of a terminal, if an electric current of 10 A is flowing through it having resistance of 20Ω.
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All appliances don’t follow ohm’s law
It depends on physical factors of the conductor like temperature, pressure
Both A and B
A
B
C
Q3. Why ohm’s law is not a universal law?
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All appliances don’t follow ohm’s law
It depends on physical factors of the conductor like temperature, pressure
Both A and B
A
B
C
Q3. Why ohm’s law is not a universal law?
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Q18. What is the potential difference between the ends of a conductor of 16 ohm resistance, when a current of 1.5 A flows through it?
ANSWER : 24 V
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Remember Resistance?
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Remember Resistance?
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How is resistance caused?
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Electrons Atoms
Impurities All of these
A B
C D
Q4. What kind of particles is present inside a conductor?
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Q4. What kind of particles is present inside a conductor?
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Q4. What kind of particles is present inside a conductor?
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Electrons Atoms
Impurities All of these
A B
C D
Q4. What kind of particles is present inside a conductor?
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Electrons Protons
Impurities Neutrons
A B
C D
Q5. Which one of the particles moves when potential difference is applied across it?
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Q5. Which one of the particles moves when potential difference is applied across it?
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Electrons Protons
Impurities Neutrons
A B
C D
Q5. Which one of the particles moves when potential difference is applied across it?
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Liar ! Chal Jhute!! Yes! Hoga Sir!
A B
Q6. Do you think electrons have eyes?
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Liar ! Chal Jhute!! Yes! Hoga Sir!
A B
Q6. Do you think electrons have eyes?
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These electrons collide with atoms.
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These collision causes them to lose momentum and slow down.
These electrons collide with atoms.
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It’s like walking through a crowded road!
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No matter how fast you want to go you can’t gain speed.
You keep losing momentum.
It’s like walking through a crowded road!
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These collisions are the opposition to the flow of electrons.
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These collisions are the opposition to the flow of electrons.
This collision is called Resistance.
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More Collision more will be the resistance.
Less Collision less will be the resistance.
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For an electron to travel a distance of 15 cm it takes 2 mins.
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For an electron to travel a distance of 15 cm it takes 2 mins.
Then how is electricity so fast?
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220 V25 V
11 V 110 V
A B
C D
Q7. With What voltage you get electricity at home?
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220 V25 V
11 V 110 V
A B
C D
Q7. With What voltage you get electricity at home?
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No Yes
A B
Q8. Is it possible to change that voltage?
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No Yes
A B
Q8. Is it possible to change that voltage?
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NoYes
A B
Q9. Does the devices like Tubelight, refrigerator and mobile phone take the same current?
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NoYes
A B
Q9. Does the devices like Tubelight, refrigerator and mobile phone take the same current?
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How can we reduce the current?
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We know, Resistance in a conductor is the result of collision in it.
Let’s see what are the factors that affect the number of collisions
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Consider 2 Hose Pipes
Less Resistance
More Resistance
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As length increases collision increases and resistance increases
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As length increases collision increases and resistance increases R ∝ l
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Less Resistance
More Resistance
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As cross section increases , space for electron increases, collision decreases, so resistance decreases
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As cross section increases , space for electron increases, collision decreases, so resistance decreases R ∝ 1/A
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Combining both,
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Combining both,
We insert a constant,
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The constant is resistivity.
Combining both,
We insert a constant,
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Resistivity is the resistance offered by a conductor of unit cross section and unit length.
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What really is resistivity?
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Ohm/ metre Ohm metre
A B
Q10. What is the SI unit of Resistivity?
Ohm/ metre2 Ohm metre2
C D
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Ohm/ metre Ohm metre
A B
Q10. What is the SI unit of Resistivity?
Ohm/ metre2 Ohm metre2
C D
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No Yes
A B
Q11. Will temperature Affect resistance?
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No Yes
A B
Q11. Will temperature Affect resistance?
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As temperature increases collision increases, Resistance increases.
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Factors A ecting Resistance are:
1. Length of the Conductor2. Cross Sectional area of the
conductor3. Resistivity of the conductor4. Temperature of the material
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V I P
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Q12. The figure shows three cylindrical copper conductors along with their face areas and lengths.Discuss in which Geometrical shape the resistance will be the highest. [2013-Boards]
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1.25 Ω 5.47 Ω
3.5 Ω 0.5 Ω
A B
C D
Q13. Calculate the resistance of 1 Km long copper wire of radius 1 mm. Resistivity of copper is 1.72 x 10-8 ohm m. [2013-Boards]
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Q13. Calculate the resistance of 1 Km long copper wire of radius 1 mm. Resistivity of copper is 1.72 x 10-8 ohm m. [2013-Boards]
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1.25 Ω 5.47 Ω
3.5 Ω 0.5 Ω
A B
C D
Q13. Calculate the resistance of 1 Km long copper wire of radius 1 mm. Resistivity of copper is 1.72 x 10-8 ohm m
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6 x 10-6 Ω m 4 x 10-6 Ω m
6.86 x 10-8 Ω m 7.06 x 10-8 Ω m
A B
C D
Q14. Resistance of a metal wire of length 5 m is 100 ohm . If the area of cross-section of the wire is 3 x 10–7 m2, calculate the resistivity of the metal. [2019 Boards]
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Q14. Resistance of a metal wire of length 5 m is 100 ohm . If the area of cross-section of the wire is 3 x 10–7 m2, calculate the resistivity of the metal. [2019 Boards]
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6 x 10-6 Ω m 4 x 10-6 Ω m
6.86 x 10-8 Ω m 7.06 x 10-8 Ω m
A B
C D
Q14. Resistance of a metal wire of length 5 m is 100 ohm . If the area of cross-section of the wire is 3 x 10–7 m2, calculate the resistivity of the metal. [2019 Boards]
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Doubled Halved
Four times One fourth
A B
C D
Q15. The area of cross section of wire becomes half when its length is stretched to double.The new resistance of wire becomes
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Q15. The area of cross section of wire becomes half when its length is stretched to double.The new resistance of wire becomes
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Doubled Halved
Four times One fourth
A B
C D
Q15. The area of cross section of wire becomes half when its length is stretched to double.The new resistance of wire becomes
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Q16. The area of cross section of wire becomes half with change in volume. The new resistance of wire becomes
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Q17. V I graph of two wires A and B are shown in the figure.If both wires are of same length and same thickness, which of the two is made of material of high resistivity. [2014-Boards]
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Q18. Length of a copper wire is 1 m and its cross sectional area is, 0.001 m2. Calculate the resistance of the wire if resistivity of copper is 1.62 x 10-8 ohm m.
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