P3 Electricity Flashcards
What is charge?
Charge is a property of matter, bodies have coulombs of charge positive, negative or neutral. Electrons carry the smallest charge 1.6x10^-19. As electrons are hard to count, coulomb’s are used to calculate PD and current. There a 6.24x10^18 electrons in a coulomb.
What links current, charge and time?
What links energy, PD and charge?
What links charge, current and resistance?
What links power, current and voltage?
Current (amps) = Charge (coulombs)/Time (seconds)
PD (volts) = Work Done (joules)/Charge (coulombs)
PD (volts) = Current (Amps) * Resistance (ohms)
Power (watts) = Current (Amps) * Voltage (volts)
What is current, voltage, potential difference and resistance?
Current is the rate of flow of charge. Voltage is a measure of energy carried by current per coulomb of charge between two points = Potential difference. Resistance is the opposition of charge and the reason current transfers energy; more resistance = more energy.
How is current, voltage and resistance related in series?
The current through every component is the same.
The total resistance is the sum of all the component resistances.
Resistance is shared across components in the ratio voltage is shared across components.
The voltage is shared across the components.
How is current, resistance and voltage related in parallel?
Potential difference across the components is the same as the power source.
The total resistance is 1/Rt = 1/R1 + 1/R2 …
The current is split between the components/branches.
What is an I-V graph? What is Ohm’s law?
An I-V graph plots current (y axis) against PD (x axis) and thus the gradient is the resistance. A steep gradient is a small resistance, a shallow gradient is large resistance.
Ohm’s law says PD is directly proportional to current when temperature is constant.
How do you investigate how the resistance of a component?
Connect all components to the power supply. Ammeter in series and voltmeter in parallel across the device you investigate.
Change the resistance of the variable resistor and register readings of ammeter and voltmeter.
Plot I-V graph and draw conclusion on resistance.
What is the I-V graph of filament and diode?
Filament: As PD increase the current does too and this means the lamp heats positive ions and vibrate faster. Resistance increases.
Diode: Forward resistance is low but reverse resistance is high.
What are thermistors and LDRs? How do they work?
Thermistors are resistors depend on temperature. Resistance increases as temperature decreases.
LDRs are resistors depend on light intensity. Resistance increases as light intensity decreases.
How do semiconductors work with energy?
When the semiconductor receives more energy, ions vibrate faster so less electrons move through the wire (resistance increases) which is typical for a normal resistor.
However, afterwards, electrons from the atoms of the semiconductor are liberated so more move through the wire at once.
Part 2 is more drastic than part 1 so current increases, effectively meaning resistance decreases.
Equations involved with electricity
Power = Voltage * Current
Charge = Current * Time
Energy = Voltage * Charge
Voltage = Resistance * Current
How do you produce static electricity? How do you discharge an object?
When you rub two insulators together, you can transfer electrons with friction. The charge caused by the transfer of electrons is static electricity.
To discharge an object, you allow the charge to move by connecting it to a conductor. Sparks also discharge.
