physics p4 Flashcards
revision
what happens when you rub 2 insulating materials together?
Electrons are transferred from one material to the other - this is called STATIC ELECTRICITY
In an experiment, an insulator becomes negatively charged when it is rubbed with a dry cloth.How (in terms of electrons) did it become charged?
Electrons are transferred from the cloth to the insulator.Electrons are negatively charged and so when an insulating material gains electrons, it becomes negatively charged.
why does the insulator not lose its charge?
Insulators do not allow electrons to flow through them and so the negative charge cannot flow from the insulator hence why it does not lose its charge.
Does a charged particle create a field around itself + how are field lines drawn ??
Yes a charged object does create a field around itself and field lines are drawn from positive to negative.Also == the greater the distance between the charged objects,the smaller the force between them.
what does an LDR do?
An LDR changes its resistance according to the light level
What does a resistor do ?
Restricts the flow of current
what does a variable resistor do?
A variable resistor allows the user to change the flow of current
what does a diode do ?a
A diode allows the current to flow in one direction only
what does a LED do???
A LED allows the current to flow in one direction only and EMITS LIGHT WHEN CURRENT FLOWS THROUGH IT
What does a fuse do?
A fuse melts and therefore “breaks” the current when the current is grater than a certain amount
What is Current?
Current is the RATE OF FLOW OF CHARGE - and is charge
What does the charge through a component depend on?
THE current through a component depends on : the resistance of the component and the pd across the component
what is P.D or POTENTIAL DIFFERENCE?
POTENTIAL DIFFERENCE is the difference in energy before and after a component
What measures P.d OR VOLTAGE
A voltmeter measures pd and is always connected in a parallel with the component
What is resistance?
Resistance is the opposition to current flow
what is Ohms law?
Ohms law states that the current through a resistor at a constant temperature is directly proportionate to the P.D across the resistor == components that behave like this are called OHMIC CONDUCTORS.
what does reversing the p.d across a resistor do to the current
reversing the p.d through a resistor reverses the current through it
what does it show if the current/pd line for a filament lamp is a fancy f
The current is not directly proportionate to the P.D because the line is a curve
Explain the pd/current graph for the filament lamp
The current/pd graph line for a filament lamp is an f because ;; ==
The resistance increases as the current increases.So the resistance increases as the temperature increases .The atoms in the metal filament vibrate more as the temp increases.So they{the atoms} resist the passage of the electrons more.
Explain the P.D/current graph for a Diode
The current through the diode is in one direction only. In the reverse direction,the diode has a very high resistance — so the current through the diode is virtually is virtually zero.
Thermistor
Resistance decreases as the temp increases
Light Dependant Resistor (LDR)
the resistance decreases as the light intensity on it decreases.
Series circuits
In series Circuits==:
The CURRENT is the SAME in EACH COMPONENT
the TOTAL P.D is SHARED between the COMPONENTS
ADDING the COMPONENTS RESISTANCE gives TOTAL RESISTANCE
Adding more resistors in SERIES
Adding more resistors in series increases total series because the current through the resistors is reduced and the P.D across them is unchanged
series circuits total resistance
R(total) == R(1) + R(2)
Why is current the same in series circuits?
Current is the same in series circuits because
the current must flow through both of them meaning that the total resistance is the sum of the individual components resistances
parallel circuits
Total current == SUM OF THE CURRENTS through the SEPERATE COMPONENTS
the PD across EACH COMPONENT is the SAME
The total resistance of 2 (or more) components is LESS than The component with the least resistance.
SERIES CIRCUITS RESISTANCE
Adding more resistors in a series circuit decreases total resistance because the current flowing through he resistors is increased and the P.D across them is unchanged
