Electric Current Flashcards
What is current
Passage of charge particles
What is the conventional direction of current
From positive to negative
What is potential difference
Work done per unit charge
What is resistance
Voltage / Current
What is Ohm’s Law
Pd across a metallic conductor is proportional to the current through it
What is the unit for resistivity
Ohm metre
What is a superconductor
A wire made of material that has zero resistivity at and below a critical temperature
What are superconductor used for
Making high-power electromagnetic for very strong magnetic fields
What does a heater on a circuit look like
Four squares
What does an electric motor look like on a circuit
Circle with M in the middle, with line under it
Describe the I/V graph for a wire
y=x
Describe the I/V graph for a filament lamp
Slanted s
Describe the I/V graph for a diode
No current below 0 volts, then large peak after a few volts
When does resistance in a wire increase
When temperature increases, causing positive ions to vibrate more and stop charge carries from passing through
What are thermistors used for
Temperature sensors
How do thermistors work with increases temperature
Increased temp decreases resistance
What is a potential divider
A combination of resistors in series connected across a voltage source to produce a required pd
What is equation for energy dissipation per time
This is P = IV
Define emf
Electrical energy produced over unit charge
What is internal resistance
Resistance of materials within a battery
What is the difference between emf and potential difference
Emf is energy converted from chemical to electrical.
Voltage is energy converted from electrical to other forms
How to determine the emf and internal resistance of a battery
Measure V and I across a resistor, change R and repeat, draw graph of V vs I, emf is y-intercept and internal is negative gradient
What is the equation involving emf
V = emf - Ir
Why is measured voltage not equal to emf
Battery has internal resistance, current passes through this, work is done and volts are lost
