6-3 Law of ohm (6.2 p 226)

Law of ohm (p 226)




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- Calcualtor
- iPad

Mark
- NO


Lessonup
- YES
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Slide 1: Diapositive
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Law of ohm (p 226)




Stationary
- Writing book
- Pen, pencil
- Calcualtor
- iPad

Mark
- NO


Lessonup
- YES
Schoolbags in
the cupboard
Phones in the phone bag

Slide 1 - Diapositive

Lesson goals:
  • Give ohms law in words and 
       in a formula.
  • Draw graphs showing conductors adhering to ohms law and conductors that dont adhere to ohms law.
  • Explain what an NTC and LDR is
And then you will do a practical where you draw graphs of a lightbulb and a resistor.

Slide 2 - Diapositive

Ohm's law
The voltage across a conductor and the current through a conductor are directly proportional if the resistance remains constant.


Slide 3 - Diapositive

Direct proportionality

As one amount increases, the other amount increases at the same rate.


Slide 4 - Diapositive

Slide 5 - Lien

What is the relationship between voltage and current?
A
Linear relationship
B
Directly proportional
C
Inversely proportional
D
Proportional relationship

Slide 6 - Quiz

What is the relationship between the current and the resistance?
A
Linear relationship
B
Directly proportional
C
Inversely proportional
D
Proportional

Slide 7 - Quiz

What is the unit for voltage?
A
Ampere
B
Volt
C
Ohm
D
Kilogram

Slide 8 - Quiz

The resistance in a circuit remains constant. At a voltage of 1,7 V the current is 3,5 A. What is then the current at a voltage of 5,1 V?
A
1,2 A
B
2,5 A
C
8,3 A
D
10.5 A

Slide 9 - Quiz

The resistance in a circuit remains constant. At a voltage of 1,7 V the current is 3,5 A. What is then the voltage at a current of 5,6 A?
A
1,1 V
B
2,7 V
C
2,9 V
D
3,2 V

Slide 10 - Quiz

Explain what a direct proportionality is.

Slide 11 - Question ouverte

NTC - negative temperature coefficient
An NTC is sensitive to changes in temperature. If the temperature rises the resistance decreases.

Uses: prevents overheating in electronic
appliances like computers and
amplifiers.

Slide 12 - Diapositive

LDR - Light dependent resistor
Sensitive to changes in light. More light results in less resistance.

Uses: As a switch in a nightlamp

Slide 13 - Diapositive

An NTC is sensitive to changes in
A
temperature
B
light
C
current
D
voltage

Slide 14 - Quiz

Now do experiment 2 and 3 (p247 and 248)

Rules:
- Work in groups of 2 or 3
- It is not for a mark.
- Important to have the graph of U vs I
for the lightbulb and the resistor done
in 20 minutes.
timer
20:00

Slide 15 - Diapositive

Resistance and temperature
With an incandescent lightbulb
there is a deviation from the 
direct proportionality.

The reason is the high temperature of
the filament. The higher the temperature
the greater the resistance.

Slide 16 - Diapositive

What did you
learn today?

Slide 17 - Carte mentale

Homework
Test yourself 6.2

Slide 18 - Diapositive