Physics- Resistance + Ohm's law Flashcards
(14 cards)
What is an electric current?
An electric current is a flow of charged particles around a circuit.
What are the charged particles in a circuit and how do you know if a material is a good conductor of electricity?
Typically, the charged particles in a circuit are electrons and a material is a good conductor of electricity if it has a lot of free electrons.
How is the ammeter placed with the component of interest?
The ammeter is always placed in SERIES with the component of interest- meaning it’s connected in a direct line with the component or circuit whose current is being measured.
What is the ‘voltage’ in a circuit?
The ‘voltage’ in a circuit is a measure of how much energy is transferred from the electrons to the components. It’s also a measure of the energy given to charge carriers in a circuit. It’s essentially the “push” that causes electricity to flow.
How is the voltmeter placed with the component of interest?
The voltmeter is always placed in PARALLEL to the component of interest- this means that the voltmeter is connected across two points in a circuit, sharing the same voltage as those points.
What is potential difference?
Potential difference is pretty much synonymous to voltage but is more referred to as the difference in energy either side of the component.
If there is more resistance…
less current will flow
Why may resistors reduce the current flowing around the circuit?
-To protect other components
otherwise, resistance is simply a property of the circuit- even the wires have a small resistance
How does the length and thickness of a wire affect it’s resistance?
Longer and thinner wires provide more resistance.
- The longer a wire, the greater its resistance cs If the wire is longer, each electron will collide with more metal ions, and so there will be more resistance:
-The thicker the wire, the lower the electrical resistance because there is more space for the electrons to flow through.
This means that a thicker wire will allow more current to flow through it than a thinner wire of the same material and length.
What is Resistance measured in?
Resistance is measured in Ohms. (omega symbol).
Write the equation for resistance and rearrange it:
Resistance = Voltage / Current
R = V/I
Current = Voltage / Resistance
Voltage = Current x Resistance
What is Ohm’s Law?
Ohms law describes the relationship between current, voltage and resistance.
‘Current is directly proportional to Voltage but inversely proportional to Resistance’
This is bc a higher voltage means more “push” for electrons moving in a circuit, leading to a greater flow of charge (current), and more resistance is less current.
Write up the method for the required practical: Measuring Resistance:
AIM:
To complete an experiment to measure the values of some resistors with unknown resistance values.
METHOD:
Arrange the power pack, resistor and ammeter and connect one to the next in series. Connect the Voltmeter last, either side of the resistor (to measure the potential difference across it, in parallel).
-Adjust the power pack to give eight different voltages; record these values with the corresponding currents in your table. Repeat the experiment for the other resistor.
Drawing the Graph:
Although Current is the dependent variable, we know that R = V/I , so reversing the axes leads to the gradient being equal to the unknown resistance value. SO then draw a graph of PD (y-axis) against current (x-axis); plot both sets of data on the same axes, joining each set of points with a line of best fit.
Find the gradient of each line, and quote the resistance of each resistor.
Extra info
(All voltages given to 2dp; all currents given to 2dp, Points are plotted to the nearest 1mm., Both axes are labelled with the variable and unit.)
Graph: The steeper the line the…
greater the Resistance cs if a larger voltage is required to produce the same current, then something must be resisting the current… ELECTRICAL RESISTANCE!
Also, the less current, the higher the Resistance.
