Electricity Flashcards
Relationship between power, current and voltage
P = I x V
Power (W) = current (A) x voltage (V)
Relationship between current, energy transferred, voltage and time
Energy transferred (J) = current (A) x voltage (V) x time (s)
E = I x V x t
relationship between resistance, current and voltage
Voltage (V)= current (A) x resistance (Ω)
V = I x R
relationship between current, charge and time
Charge (C) = current (A) x time (s)
Q = I x t
relationship between charge, voltage and energy transferred
energy transferred (J) = charge (C) x voltage (V)
E = Q x V
How does insulation and double insulation work?
Insulation
- wires are covered with an insulating material
- non-metallic case that acts as a second layer of insulation (double insulation)
How does earthing work?
- Additional safety wire
- earth wire links the casing to the energy source
- when the live wire touches the casing, current flows through the casing and along the earth wire to complete the circuit
How do Fuses work?
- safety device to cut off the flow of electricity when current becomes too large
- usually a glass cylinder containing a thin metal wire
When current is too large - wire melts, causing the wire to break and stopping the current
How do circuit breakers work?
- automatic electromagnet switch that breaks the circuit when current exceeds
+ does not melt / break
+ reusable
+ fast
What is direct current?
Current that continuously flows in the same direction
What produces direct current?
Electric cells or batteries
What is alternating current?
Current that constantly changes direction
What kind of terminal does direct current have?
Positive and negative terminal
What kind of terminal does alternating current have?
2 identical terminals
What produces alternating current?
Electrical generators (main electricity)
Why does current in a resistor increase temperature?
- When electricity passes through a resistor some of the electrical energy turns into heat
- electrons collide with ions in the lattice that make up the resistor as they flow through, giving ion energy, causing it to vibrate and heat up
2 advantages of a series circuit
- All of the components can be controlled by a single switch
- Fewer wires are required
2 Disadvantages of a series circuit
- Components cannot be controlled separately
- If 1 component breaks the rest will stop working as well
2 advantages of a parallel circuit
- Components can be individually controlled
- If a component breaks, others will continue to function
2 Disadvantages of a parallel circuit
- More wires are required
- All components have the same voltage as the supply, (harder to control if components need diff. voltages)
What 2 things does the current in a series circuit depend on?
- voltage of the power source
- Number and type of components in the circuit
What is the effect of changing resistance on the current in a circuit
As resistance increases, current decreases
How does the resistance of LDRs change with light intensity?
As light intensity increases the resistance of an LDR decreases
How does resistance of a thermistor change depending on temperature?
As temperature increases the resistance of a thermistor decreases
What does adding lamps or LEDs to a circuit indicate?
Presence of a current
What is current
the rate of flow of charge
What does current do at a junction?
Current ‘splits’ to take both paths.
It comes back together when the paths meet again.
e.g - I1 = I2 + I3 +I4
What happens to voltage across 2 components connected in parallel
The voltage is equal
VT = V1 = V2
How do you calculate the currents of 2 resistive components connected in a series circuit
IT = I1 = I2
How do you calculate the voltage of 2 resistive components connected in a series circuit
VT = V1 + V2
How do you calculate the resistances of 2 resistive components connected in a series circuit
RT = R1 + R2
what is voltage
voltage is energy transferred per unit charge passed
V = energy transferred (J) / charge (C)
