Physics - Resistance and Ohm's Law

Created: January 20, 2021

What is Ohm’s Law?

The current through an ohmic conductor is proportional to the potential difference across it when at a constant temperature.

What is the symbol formula for resistance?
\[R = \frac{V}{I}\]

What is the word formula for resistance?
\[\text{resistance} = \frac{potential difference}{current}\]

What is the formula for potential difference $V$ in terms of resistance $R$ and current $I$?
\[V = IR\]

What is the formula for current $I$ in terms of resistance $R$ and potential difference $V$?
\[I = \frac{V}{R}\]

What are the units for resistance?

Ohms, $\Omega$

What does $1\Omega$ mean?

The resistance of a component when a potential difference of $1V$ is produced per ampere of current.

In an Ohmic conductor, what happens if you double the potential difference?

The current also doubles.

How can you tell from a voltage-current graph that something is an Ohmic conductor?

The line is linear.

How could you describe resistance in a component?

The amount that a component resists the flow of charge carriers through it.

What is the resistance of a component $R$ defined as?

The ratio between $V$ and $I$.

PHOTO VOLTAGE RESISTANCE GRAPH Which of these components is an Ohmic conductor?

B

PHOTO VOLTAGE RESISTANCE GRAPH Which of the components shows a decreasing resistance at higher currents?

A

2021-01-22

What is an Ohmic conductor?

A component where the current is always directly proportional to the potential difference.

What is the threshold voltage in a diode?

The voltage at which a diode starts letting current through.

PHOTO RESISTOR IV CHARACTERISTIC What component is this?

A resistor.

PHOTO RESISTOR IV CHARACTERISTIC How can you tell this component in an Ohmic conductor?

The current is directly proportional to the potential difference.

PHOTO RESISTOR IV CHARACTERISTIC What is the gradient equal to?
\[\frac{1}{R}\]

What is on the $y$-axis of an $IV$ characteristic?
\[I\]

What is on the $x$-axis on an $IV$ characteristic?
\[V\]

PHOTO LARGER RESISTANCE Which graph, left or right, has a higher resistance?

Left.

Why does a smaller gradient mean a larger resistance?

Because the gradient is $\frac{1}{R}$ it’s the opposite to what you expect.

PHOTO FILAMENT BULB IV CHARACTERISTIC What component is this?

A filament bulb.

PHOTO FILAMENT BULB IV CHARACTERISTIC How can you tell that this component is not an Ohmic conductor?

The current is not directly proportional to the potential difference.

PHOTO FILAMENT BULB IV CHARACTERISTIC What happens to resistance as voltage increases?

It begins to increase.

PHOTO LED IV CHARACTERISTIC What component is this?

A diode.

PHOTO LED IV CHARACTERISTIC Effectively, what is the resistance on the left hand side of the graph?
\[\infty\]

PHOTO LED IV CHARACTERISTIC Is a diode an Ohmic conductor?

No.

PHOTO IV DATA COLLECTION CIRCUIT What is this circuit used to measure?

How current varies with voltage.

PHOTO FILAMENT BULB IV CHARACTERISTIC How can you take data for “negative voltages”?

Flip the polarity of the battery.

2021-03-02

In series, what is the formula for the total resistance $R _ T$ given $R _ 1, R _ 2, R _ 3, …$?
\[R_T = R_1 + R_2 + R_3 + ...\]

In parallel, what is the formula for the total resistance $R _ T$ given $R _ 1, R _ 2, R _ 3, …$?
\[\frac{1}{R_T} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + ...\]


Related posts