I–V Graphs Flashcards

All 6 cards in this deck

What does a straight line through the origin on an I–V graph tell you about a component?

It is linear (ohmic): current is directly proportional to pd, so resistance is constant.

What does a curved I–V graph tell you about a component?

It is non-linear (non-ohmic): its resistance changes as the current changes.

What is the shape of the I–V graph for a filament lamp?

An S-shaped curve through the origin that gets less steep as the pd increases, because resistance rises with temperature.

What is the shape of the I–V graph for a diode?

Almost zero current in the reverse direction, and current rising steeply only after a small forward pd.

What are the steps to determine the resistance of a component at one point on its I–V graph?
e.g. at a pd of $1.0$ V the graph gives $I = 0.08$ A

1. Read the current at that pd: $I = 0.08$ A
2. Rearrange $V = IR$ to $R = V/I$
3. Substitute: $R = 1.0/0.08 = 12.5\ \Omega$

True or false? The resistance of a component at a point on its I–V graph is equal to the gradient of the graph at that point.

False. Resistance is $V \div I$ at that point; for a straight line through the origin the gradient is $1/R$.