Phyiscs Ka2 Flashcards
Where are semi conductors found?
On the boundary between metals and non-metals
Why is silicone a semi conductor?
Because it doesn’t have energy, they behave like insulator but with no free electrons. When we put in light they release electrons
What is a diode?
A diode is made of two pieces of semi-conductor, treated so the electrons will only flow directly across the boundary.
What happens to a diode in a circuit?
It allows current to flow easily on the forward direction, but not in the reverse direction
The sum of the p.d of the components in a series circuit = ???
The supply p.d (Vs = V1 + V2)
In a parallel circuit the p.d across each component = ???
The battery P.d (Vs = V1 = V2)
What is the striped wire and where is it?
The earth wire and at the top
What is the brown wire and where is it?
The live wire and on the right
What is the blue wire and what is its charge?
The neutral wire and on the left
What are the pins made of in a plug and why?
Brass because it is a good conductor and it is strong so it doesn’t bend and also won’t rust
What is the body of the plug made from and why?
Plastic because it is a good insulator
Why does the fuse melt?
When the current is too large so the circuit does not break
What does the cable grip in a plug do?
Stops the wire from being pulled out of place
What happens to the resistance of a filament lamp as the temperature of the filament increases?
It increases
A diode has a very ____ _____ in the reverse direction
High
What happens to the resistance of a light dependent resistor as the light intensity increases?
It decreases
Explain what happens to the lamp in the thermistor circuit
The brightness of the lamp increases as the current increases and the resistance decreases
Explain what must happen to the resistance in the LDR
The resistance decreases as the light intensity increases
Explain what must happen to the lamp in the LDR circuit
The brightness will increase as the resistance decreases and the current increases
In a series circuit, the ____ is the same value at any point in the circuit
Current
In a parallel circuit the _____ of the current in each loop is equal to the _______ _______
Sum, current total
In a _____ circuit each loop has the ____ P.d across it
Same
What is the equation for power and what is it measured in?
Power= energy / time
Measured in W
1W = _____
1J/s
What is the equation for power in electricity?
Power = p.d x current
What happens if the live in a washing machine is damaged?
The case will become live. The earth wire provides a low resistance path for the current to flow from the live wire
What is an alternating current? (A.c)
Repeatedly reverses its direction. If flows one way then the other. It’s frequency is the number of cycles it passes through each second
How much altering potential difference does a typical power station generate?
25000V
When are step up transformers used
At power stations to transfer electricity to the national grid
When are step down transformers used?
To supply electricity from the national grid to the consumers
Why make the grid potential difference very large?
Much less current is needed to transfer the same amount of power, so the power loss due to the resistance hearing the cables is much reduced. This means the national grid is an efficient way to transfer power
When is an oscilloscope used?
To show how an alternating potential difference changes with time
The uk mains supply is about ____ volts
230
Why does a mains cable have two or three inner cores of copper?
Because it’s a good conductor
How much potential difference do the step up and step down transformers produce?
123000V
What is the national grid?
The system of cables and transformers
What happens to the electricity produced when a power station passes through a transformer
The voltage increases (step up transformer)
What happens to the electricity when it reaches houses or factories?
It must have the voltage reduced (step down transformer) before it can be used safely
Why do we use a high voltage in the cables?
To improve efficiency and reduce the waste heat
When a current passes through it has a _____ heating effect. Energy is transferred from _____ to ______.
Heating, electrical, thermal
The larger the _____ the lower the ______
Transfer, efficiency
If we reduce the _____, by increasing the _____, the transmission system is more _______
Current, voltage, efficiency
Power loss in a cable = ???
Current² x resistance
The p.d of a battery is the ____ supplied to each _____ of _____ as it passes through the battery
Energy, coulomb, charge
What is the equation for charge flow?
Charge flow= current x time
What is the equation for energy transferred?
Energy transferred = charge flow x p.d
What is the equation for total resistance?
Resistance total= R1 + R2
What is the equation for potential difference?
P.d = current x resistance
