P2.4 Flashcards
Why does a TV screen crackle when switching it on?
Charged with static electricity so it becomes electrically charged.
What subatomic particles are in the nucleus of an atom?
Protons and neutrons.
Where are the electrons in an atom?
Moving about in the space around the nucleus.
What is the charge of each subatomic particle?
Protons-positive
Neutrons-no charge
Electrons-negative
What is an uncharged atom?
Atom that has equal number of protons and electrons.
What is a charged atom called?
An ion.
How do some insulators become charged?
By rubbing them with a dry cloth.
What happens when you rub a polythene rod with a dry cloth?
It transfers electrons to the surface.
What happens when placing two objects with the same type of charge next to each other?
They repeal each other.
What happens when you place two objects that have different types of charge next to each other?
They attract each other.
What does a circuit diagram show?
Shows us how the components in a circuit are connected together.
What is an electric current?
Flow of charge.
What happens when an electric torch is on?
Electrons pass through the torch bulb and through the cell every second.
What do the electrons do to the positive ions in a metal?
Stops he ions from moving away from each other.
Why do the electrons pass through the bulb?
Because its filament is made of a metal.
What do the electrons transfer and to where?
Transfer energy from the cell to the torch bulb.
What is the size of an electric current?
The rate of flow of electric charge.
Per second
What happens if you increase the number of electrons passing through a component?
The current passing through it becomes bigger.
What is the electric charge measures include?
Coulombs (C)
What is an electric current measured in?
Amperes (A) or amps
What is the rate of flow of charge if the electric current is 1 amps?
It’s also 1 coulomb.
What is the equation for the current in amps?
=charge flow in coulombs/time taken in seconds
What is the equation for the potential difference across the component in volts?
=work done in joules/charge in coulombs
What is he equation for resistance?
=potential difference(volts)/current(amps)
What do the electrons have to do?
Push their way through lots of vibrating ions in the metal filament then the ions resist the passage of electrons through the torch bulb.
What is he unit of resistance?
Ohm
What does the resistor limit?
The current.
What is the current throughout resistor at constant temp directly proportional to?
To the potential difference across the resistor.
Why do we say a wire is ohmic conductor?
Because its resistance is constant.
Why doesn’t reversing the pd make a difference to the shape of the line?
Because the resistance is the same whichever direction current is in.
What does a straight line through the origin mean?
That the current is directly proportional to the potential difference.
The resistance is constant.
If the line curves away from the axis what does it say about the current?
Not directly proportional to the potential difference.
What happens to the resistance if the current increases?
It increases.
Why does the resistance increase as the the temperature increases?
Because the ions in the metal filament vibrate more as the temperature increases.
In the forward direction, how is the line in a diode graph? What happens to the current?
Line curves towards the axis.
Current is t directly proportional to the potential difference.
In the reverse direction, what is he current in a diode graph? What happens to the resistance?
Current is negligible.
Resistance in the reverse direction is much higher that in the forward direction.
What does a thermistor show?
Shows the current-potential difference graph at two different temperatures.
What does a light-dependent resistor show?
Shows the current-potential difference graph in bright light and in dim light.
Why does the same current pass through components in series with each other?
Because the same number of electrons are passing through each component every second.
What is the potential difference of a cell?
It’s a measure of the energy transferred from the cell by each electron that passes through it.
When is the rule, the potential difference of the cell is shared between the bulbs, applied?
When each electron in the circuit goes through both bulbs.
What happens to the potential difference when the cells act in the same direction?
The total potential difference of cells in series is the sum of the potential difference of each cell.
What happens when we use two or more cells in series in a circuit?
Each electron gets a push from each cell provided that each cell is connected so they act in the same direction.
What does the share of the cell’s potential difference across each component depend on?
Depends on the setting of the variable resistor.
What is the equation for the resistance?
= R1 + R2
What is the total resistance of components equal to?
Equal to the sum of the resistance of each component.
What is a bypass?
A parallel route.
What rule is applied when components are in parallel?
The current through the cell is equal to the sum of the currents through the two bulbs.
What is the potential difference for components in parallel?
Potential difference across each component is the same.
What is the equation for the current?
=potential difference(volts)/resistance(ohms)
What happens to the current if the resistance becomes bigger?
The current through it becomes smaller.
Which resistor passes the smallest current?
The ones that have the largest resistance.
