| What is resistance? | the opposition to current
when material opposes charges flowing through it when current is passing through |
| What is resistance measured in | Ohms - Ω |
| do good electrical conductors have a high or low resistance? | low resistance |
| do thicker objects have a higher or lower resistance | lower resistance |
| do thinner objects have a higher or lower resistance | higher resistance |
| as length increases, does resistance increase or decrease | resistance increases |
| as temperature increases, does resistance increase or decrease? | resistance increases |
| what does Ohm's law describe? | the relationship between the current through an object and the voltage across it |
| describe the ohm's law experiment | set up a circuit with a dc power supply, a resistor and ammeter in series and a voltmeter in parallel to the resistor.
set power supply to 1V and turn it on.
measure the current through the resistor with ammter.
measure the voltage across the resistor with a voltmeter
note these values in a table
repeat steps 3-5 increasing the pwoer supply by 1V each time until you reach 10V
draw a graph of voltage on y axis and current on x axis
compare the graphs gradient with the resistor values
repeat for other resistor values
If the lines gradient matches the value of the resistor then Ohm's law has been verified. |
| when drawing a graph of voltage against current, where should the line of best fit cross? | line of best fit should go across the origin as the relationship between voltage and current is directly proportional |
| say you've set up a circuit with a power supply and a resistor in series.
what will happen if you leave the power supply on for too long? | the resistor will heat and become non-Ohmic |
| what is a non-Ohmic conductor | an electrical conductor that increases its resistance as it gets wwarmer
a conductor in which the resistance will change
for resistors, it will increase. |
| give two examples of non-ohmic conductors | filament lamps
LEDs |
| what will happen to the line of best fit on a voltage/current line graph when using a non-Ohmic conductor? | the line of best fit will be curved.
this can be prevented by letting the resistor cool between readings |
| on a voltage/current line graph, what could cause a line of best fit to not go through the origin. what does this mean? | straight line of best fit that doesn't go through the origin means the relationship between V/I is linear but not directly proportional.
This could happen for low values of resistance as the resistance of the whole circuit can become significant. |
| What does Ohm's law specifically state? | the current in a conductor at a constant temperature is directly proportional to the potential difference across it. |
| what formula can you use to calculate resistance using Ohm's law? | V=IR |
| describe in detail why/how resistance of a conductor can increase with temperature | if a device is operating with a high current for a long time it will heat up. as temperature increases, atoms within the conductor begin to vibrate more. Moving electrons in the conductor may collide more often with vibrating ions. these act as barriers to the flow of charge, increasing the electrical resistance. |
| give two examples of non-ohmic conductors | filament lamps
LEDs |
