 So in this video, we're going to look at two different types of components. They're called ohmic and non-ohmic materials So ohmic materials are materials that always follow Ohm's law that V equals IR But we could rearrange this so instead it says R is equal to V over I These materials always have the same resistance under all conditions therefore if we were to create a plot of voltage against current as Shown here. So on the y-axis. We have potential difference or voltage and on the x-axis We have current and we would get a straight line and note that because the resistance is equal to the voltage Divide by the current the resistance will be the slope of the graph In this plot just next to it We can see that as we increase the voltage we increase the current and it is linear. It's directly proportional The problem is that not all materials obey Ohm's law and these materials are called non-ohmic This means that their resistance is not always constant For example, if we consider a light bulb like here a Graph of the voltage and the current would look something like this one here So as the voltage increases the current still increases, but not quite in a straight line That's because as the voltage starts to get quite high the current gets quite high And this causes the resistance to increase and so the current starts to drop off So in this particular case for our non-ohmic material the current is lower than what it would have been for an ohmic material at these high voltages Another example of a non-ohmic material is a diode So a diode is an electronic component that only allows voltage to flow one way So here's a plot of current against voltage of a diode So we can see that first Negative voltages. There is essentially no current at all. No current will flow through the circuit So the resistance is extremely high for a negative voltage However, it only takes a small positive voltage to induce a current in this direction It's also possible for resistance to depend on other factors. For example, there are light dependent resistors and thermistors So a light dependent resistor changes resistance when exposed to light of different intensities If we included a light dependent resistor in a circuit, it would behave differently in the light than in the dark So this would be extremely useful if we wanted to make a device turn on or off at night time For example in street lamps and so we can see that as the light intensity increases the resistance decreases So similar to a light dependent resistor a thermistors resistance also changes. However, it changes when the temperature changes So a thermistors resistance depends on temperature This is an extremely useful property because it effectively allows a circuit to measure temperature So a circuit containing a thermistor would work differently at high temperature Compared to in a low temperature So this would be really helpful if we wanted to build a heater that automatically turns off when it's warm So to summarize, ohmic materials are materials that follow Ohm's law that V equals IR However, there are a range of electronic components and materials that do not follow Ohm's law and many of these have useful properties Thank you very much