P3 Flashcards
What is the build up of static caused by?
Transferring electrons.
What is the force between two charged objects called?
Electrostatic attraction.
How could you test whether an object is charged?
Explain how it works.
Holding a charged rod above small scraps of paper. The charged rod induces a charge in the paper (if it is positively charged), attracting the electrons in paper towards it and repels it if negative.
Explain how you could test for charge using a gold leaf electroscope.
Negative charged insulator: charge is transferred to the electroscope, conducted down to the metal stem and gold leaf. This negatively charged both the stem and the gold leaf, causing them to repel against each other.
What direction does electric field lines go from?
Positive to negative.
State what will happen to the strength of the electric field around a uniformly charged sphere as you move towards the sphere.
The strength of the electric field increases as you move towards the sphere.
What is potential difference?
The driving force that pushes the current around.
How can you define current?
Current is the rate of flow of electric charge around the circuit.
How can you calculate total charge?
Charge = current x time
How can you calculate the energy transferred?
Energy transferred = charge x potential difference
What is the purpose of an ammeter?
How must it be placed?
It measures the current flowing through components.
It must be placed in series with the component.
What does the voltmeter do?
How must it be placed and why?
It measures potential difference.
It must be placed in parallel with the component ;
so it can compare the energy the charge has before and after passing through a component.
What is the formula for potential difference?
Potential difference = current x resistance
Explain how resistance increase with temperature.
Thermal energy store = kinetic energy store
Particles vibrate more and make it more difficult to transfer electrons through resistors -> resistance increases
Why does current only flow in one direction through a diode?
There’s very high resistance in the reverse direction.
What is a thermistor and how does it function?
A temperature-dependent resistor.
The resistance drops in hot conditions and goes up in cool conditions.
How can thermistors be used in fans ?
Resistance of thermistor increases/ decreases depending on temperature and takes a bigger/ smaller share of the power supply.
How do LDRs function in bright conditions?
More light intensity: Resistance of LDR is low and takes less energy for the current to pass through -> low p.d
-brighter light is produced
Describe the state of potential difference, current and resistance within a series circuit.
Potential difference is shared.
Current is the same everywhere.
Resistance adds up.
Describe the state of potential difference, current and resistance within a parallel circuit.
Potential difference: same
Current: shared
Resistance: dependent on circuit
What is power? What is the formula related to it?
The rate of energy transfer. Energy transferred (J) = power (W) x time (s)
How could you calculate power from current and potential difference?
Power = potential difference x current
How could you calculate power from current and resistance?
Power = current^2 x resistance
