5.2 resistance

• Natuurkunde
• Middelbare school
• havo
• Leerjaar 3

Goals

5.2.1 You can explain how to determine the resistance of a wire or other component.

5.2.2 You can do calculations using the relationship between resistance, voltage and current.

5.2.3 You can explain the difference between ohmic and non-ohmic resistance.

5.2.4 You can describe how the resistance of an NTC or LDR depends on other variables.

resistance

The property of a component that determines how easily electrical current flows through it.

Ohm’s Law

The rule that says the voltage (across the wire) and the current (through the wire) are directly proportional.

A current of 20 mA runs through a 600 Ω resistor.

What is the voltage across the resistor?

Resistor

George Ohm

ohmic resistance

Resistor where the resistance is the same regardless of the voltage.

There is a voltage of 12 V across a resistor. A current of 30 mA goes through the resistor. Ohm’s law applies to this resistor.

What current would go through the resistor when the voltage is increased to 36 V?

Beth is doing a series of measurements on two wires (A and B). She has made an (I,U) diagram of her measurements.

Which wire has the higher resistance?

1. Wire A
2. Wire B
3. Impossible to say

The resistance of a lightbulb, 

ohms law does not apply

incandescent bulb

Here are the (I,U) diagrams of three resistors.

Which resistor obeys Ohm’s law?

1. Resistor A
2. Resistor B
3. Resistor C

NTC

A variable resistor that changes to the amount of themperature 

 (higher resistance when the temperature is lower)

LDR

A variable resistor that is sensitive to changes in the amount of light.

(higher resistance when the light is lower)

The resistance of an NTC is related to the temperature.

Which of the graphs correctly represents this relationship?

1. Graph A
2. Graph B
3. Graph C
4. Graph D