6-3 Law of ohm (6.2 p 226)

• Natuurkunde
• Middelbare school
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• Leerjaar 3

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

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.

Ohm's law

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

Direct proportionality

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

https:

What is the relationship between voltage and current?

1. Linear relationship
2. Directly proportional
3. Inversely proportional
4. Proportional relationship

What is the relationship between the current and the resistance?

1. Linear relationship
2. Directly proportional
3. Inversely proportional
4. Proportional

What is the unit for voltage?

1. Ampere
2. Volt
3. Ohm
4. Kilogram

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?

1. 1,2 A
2. 2,5 A
3. 8,3 A
4. 10.5 A

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?

1. 1,1 V
2. 2,7 V
3. 2,9 V
4. 3,2 V

Explain what a direct proportionality is.

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.

LDR - Light dependent resistor

Sensitive to changes in light. More light results in less resistance.

Uses: As a switch in a nightlamp

An NTC is sensitive to changes in

1. temperature
2. light
3. current
4. voltage

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.

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.

What did you
learn today?

Homework

Test yourself 6.2