Resistance & I-V characteristics Flashcards
Why does the current in a circuit change over time?
The current in a circuit changes over time because the temperature of the wire increases as a result of heating caused by the current. As temperature increases, resistance increases.
What is resistance?
Resistance is the measure of how much the material or components resists the flow of current in a circuit. Resistance opposes the flow of current, they are inversely proportional.
What is an ohm defined as?
The resistance of a component when a p.d of 1V is produced per ampere of current
Why does resistance increase when temperature increases?
- As temperature rises, the atoms in a conductor vibrate more vigorously because they gain thermal energy.
- These vibrations increase the likelihood of collisions between free electrons (the charge carriers) and the vibrating atoms.
- Each collision impedes the flow of electrons, effectively increasing resistance.
What is ohm’s law?
V = IR, for a metallic conductor kept at constant temperature, the current in the wire is directly proportional to the pd across its ends.
What are the I-V characteristics of a resistor?
The current is directly proportional to potential difference. The resistance of the resistor is constant.
What are the I-V characteristics of a filament lamp
The resistance is not constant. This is because as the current increases, there’s in increase in the amount of collisions, increasing resistance.
All components have…
All components have their own resistances.
Each components resists the flow of charge carriers through it.
It takes energy to push electrons through a component, and the higher the resistance of that component, the more energy it takes to push the electrons through it
What happens to a metallic conductor when temperature increases?
When the temperature of the wire increases, the positive ions inside the wire have a more internal energy and vibrate with greater amplitude about their mean positions.
The frequency of these collisions between the charge carriers (free electrons in the metal) and the positive ions increases, and so the charge carriers do more work/transfer more energy as they travel through the wire.
