Current electricity Flashcards
How are +ve and -ve charges carried?
+ve: (most commonly) protons
-ve: (most commonly) electrons
How do INSULATING materials become electrically charged when they are rubbed against each other?
-vely charged electrons get rubbed off from one material to the other. The receiving material gains electrons and becomes -vely charged. The other is left with an EQUAL positive charge
+vely charged protons do NOT move as they are bound by atomic forces
What is the rule about attraction and repelling, in terms of charge?
Like charges repel (- & -/+ & +), opposite charges attract (- & +/+ & -)
Define current and give an equation linking it to charge and time
A flow of electric charge, with the size of the current the rate of flow
I = Q/t [I, size of current in amperes (amps), A ; Q, charge in coulombs, C]
Define voltage and give an equation linking it to work done and charge
The voltage (OR potential difference) is the energy transferred for each coulomb of charge that passes between two points in a circuit V= W/Q [potential difference, V in volts]
What happens to a thermistor when the temperature increases?
What about when the temperature is constant?
When might a thermistor be used?
The resistance decreases
The resistance is constant
In a thermostat, to prevent heat exceeding a point
If light intensity is increased, what happens to an LDR (light-dependent resistor)?
What practical uses might one have?
Its resistance increases
Turning on street lamps when it gets dark
LEARN CIRCUIT DIAGRAMS FOR:
Switch (open and closed), cell, battery, diode, resistor, variable resistor, lamp, fuse, voltmeter, ammeter, thermistor, LDR, LED
Just do it [no images on here :( ]
Give the equation that links potential difference, current and resistance
Give current in terms of proportionality to the potential difference
V = I x R [resistance, R in ohms, Ω]
I ∝ V
Four points about components in series circuits
The total resistance is the sum of the resistance of each component
The current is the same through each component
The total potential difference of the supply is shared between the components
The potential difference is the sum of the potential difference of each cell, depending on the direction they are connected
Two points about components in parallel circuits
The potential difference across each component is the same
The total current through the whole circuit is the sum of the currents through the separate components
How and why does the temperature affect the resistance of a filament bulb?
How: resistance increases with temperature
Why: metal ions vibrate more as they get heated, which obstructs the passage of electrons through the filament as they get deflected
What does a diode do in terms of resistance?
If the diode faces forwards, the resistance is low
If it faces the other way, the resistance is very high, so that hardly any current can pass
When does an LED emit light?
Why are LEDs used increasingly nowadays?
When current flows through it in the forward direction
They use less current and are more efficient than other forms of lighting
