Paper 1 - Electricity Flashcards
What is 1V?
1 joule per coulomb
Why does a current in a resistor result in the electrical transfer of energy and an increase in temperature?
- Electrical energy is converted to thermal energy due to the resistance encountered by the moving electrons
- Increases temperature of the resistor
- Used in appliances where heat is the desired outcome
How do circuit breakers protect the device or user in domestic appliances?
- Circuit breaker opens when too much current in being carried by the wire
- Causes an open circuit
- Current cannot flow through an open/broken circuit
How does earthing protect the device or user in domestic appliances?
- Made of copper
- Low resistance path to the ground
- Connected to the casing of electrical devices
Why is current conserved at a junction in a circuit?
- Principal of conservation of electric charge
- At any point in a circuit, the number of electrons entering the junction must be equal to the number of electrons leaving the junction
How do fuses protect the device or user in domestic appliances?
- Made of a substance with a lower boiling point
- Will melt if a circuit is carrying too much charge
- Melted fuse will break the circuit so current cannot flow
What is the relationship between power, current and voltage?
P = IV
What is the relationship between energy transferred, current, voltage and time?
E = ItV
What is the difference between a.c. and d.c.?
- a.c. is main electricity being alternating current
- d.c. is electricity from a cell or battery being direct current
- a.c. is @50Hz so changes direction 50 times per second, d.c. does not
Why is a series circuit better for some appliances?
When it is ideal to have:
- Same current everywhere
- Shared voltage across components
Why is a parallel circuit better for some appliances?
When it is ideal to have:
- Shared current across components
- Same voltage everywhere
How does the current in a series circuit depend on the applied voltage and the number/nature of other components?
- Ohms law - I = V / Rtotal
- The current in a circuit is directly proportional to the voltage
- The current in a circuit is inversely proportional to the total resistance
What is the effect of changing the resistance on the current in a circuit?
- Increase in resistance = decrease in current
- Decrease in resistance = increase in current
- Current and resistance are inversely proportional
Describe the variation of resistance in LDR’s
- Increase in light = decrease in resistance
- Decrease in light = increase in resistance
- Current and light are inversely proportional
Describe the variation of resistance in thermistors
- Increase in temperature = decrease in resistance
- Decrease in temperature = increase in resistance
- Current and temperature are inversely proportional
What can lamps and LEDs be used for in a circuit?
Indicating the presence of current in a circuit
What is the relationship between voltage, current and resistance?
V = IR
What is the relationship between charge, current and time?
Q = It
What is electrical current in solid metal conductors?
A flow of negatively charged electrons
What is voltage?
The energy transferred per unit of charge passed
How does double insulation protect the device or user in domestic appliances?
- Used in appliances with plastic exteriors that do not have earthing
- 2 layers of non-conductive materials
- Only used to cover live parts
How does insulation protect the device or user in domestic appliances?
- Plastic or non-conductive material wrapped around all 3 wires
- Used to protect the appliance or user if a wire comes loose
How is the voltage across 2 components in parallel distributed?
The voltage is equal
How is the voltage across 2 components in series distributed?
It is shared between them
What is current?
The rate of flow of charge
What is the relationship between energy transferred, charge and voltage?
E = QV
How does voltage vary in wires?
- Voltage increases with current
- They are directly proportional
How does voltage vary in resistors?
- Voltage increases with current
- They are directly proportional
How does voltage vary in metal filament lamps?
- As voltage increases, the current initially increases
- But current increases at a faster rate due to the heating of the filament
How does voltage vary in diodes?
- When voltage exceeds Vf the voltage in a diode increases significantly
- The increases in not linear, it is exponential
Why does a lamp receiving more current mean that it is brighter?
- because power = current × voltage
- voltage is the same for all lamps
- current is greatest
