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Resistance & Ohm’s Law

Mahi Tuatahi / Starter

Homework booklet Electric Fields Question Five: Static Electricity


Previously we have learned about current:

\begin{aligned} & current = \frac{charge}{time} \newline & I = \frac{q}{t} \end{aligned}


and voltage:

\begin{aligned} & voltage = \frac{\text{Electric field strength}}{charge} \newline & V = \frac{E}{q} \end{aligned}


Pātai

What is the third variable that we are missing so far?


Resistance




Symbol & Units


Resistance & Heat

When current moves through a material with resistance the electrons bump into other atoms. This causes energy to be transferred in the form of vibrations (heat)!



Ohm’s Law

\begin{aligned} & V = IR \newline & voltage = current \times resistance \newline \end{aligned}



Pātai

  1. The resistance of a light bulb is $1.5k\Omega$. Calculate the current through the bulb when it is connected across a $12V$ power supply.
  2. When $9V$ is applied to a resistor, $0.03mA$ of current flows through it. Calculate the resistance of the resistor.
  3. How much voltage is required to produce $180\mu A$ of current flowing through a $0.6M\Omega$ resistor?

Whakatika Tahi

The resistance of a light bulb is $1.5k\Omega$. Calculate the current through the bulb when it is connected across a $12V$ power supply.

\begin{aligned} & V = IR \newline & I = \frac{V}{R} \newline & I = \frac{12}{1500} \newline & I = 0.008A \end{aligned}


Whakatika Rua

When $9V$ is applied to a resistor, $0.03mA$ of current flows through it. Calculate the resistance of the resistor.

\begin{aligned} & V = IR \newline & R = \frac{V}{I} \newline & R = \frac{9}{0.00003} \newline & R = 300000\Omega \end{aligned}


Whakatika Toru

How much voltage is required to produce $180\mu A$ of current flowing through a $0.6M\Omega$ resistor?

\begin{aligned} & V = IR \newline & V = (180 \times 10^{-6}) \times (0.6 \times 10^{6}) \newline & V = 108V \end{aligned}