Section 6 Electricity Flashcards
Define potential difference
Is the measure of energy transferred by each coulomb of an electron
Define resistance
How much a component/object resist the flow of current. Unit ohms
What is resistance?
The measure of how much a component/object resists the flow of current.
What is the unit of resistance?
Ohms.
What does Ohm’s law state?
V = IR - resistance.
extra info(It’s a common misunderstanding because of how the equation is written, but let’s clear it up:
Ohm’s Law, , means that:
• Voltage () is directly proportional to current (), as long as the resistance () is constant.
• Resistance () is the constant of proportionality in the equation.
If you increase the resistance () while keeping the current () constant, voltage will increase—but this doesn’t mean voltage is directly proportional to resistance! The proportionality in Ohm’s Law is between voltage and current.
For proportionality:
• Voltage ∝ Current (when  is constant).
• Current ∝  (when  is constant).
In short, Ohm’s Law focuses on the relationship between  and , not  and .)
How can you observe how current varies with p.d. for a component?
By using a variable resistor in series to change its p.d.
What is a light emitting diode (LED)?
A diode that emits light when current flows through it.
What does a straight line through the origin on an I-V graph indicate?
V and I are directly proportional.
What does a constant gradient on an I-V graph represent?
Reciprocal of resistance (R). Known as conductance
What does a steeper gradient on an I-V graph indicate?
A lower resistance.
How is resistance calculated from an I-V graph?
By picking a tangent to calculate the gradient.
What does it mean if the line curves on an I-V graph?
Resistance is not constant.
What is the behavior of diodes in terms of current flow?
Diodes only let current flow in one direction.
What happens to resistance in superconductors at the critical temperature?
Resistance decreases to 0.
What causes increased resistance in non-ohmic materials?
A larger current results in increased resistance.
What does resistivity tell us?
Resistivity tells us how resistive a material is to the flow of charge.
How is resistivity (p) defined?
Resistivity (p) is defined as ‘the resistance of a cube of unit length sides’ (unit: 5m).
What is the formula for resistance (R)?
R = pL / A
How do you measure the diameter of the wire?
Measure the diameter of the wire with a micrometer (in multiple places and calculate mean), and use to calculate cross-sectional area.
How can you change the length (L) of the wire?
Change L of wire (measure with metre rule - ensure wire is taut) by moving one crocodile clip.
What type of wire should be used for resistivity measurements?
Use wire of material for which resistivity does not change much with temperature e.g. nichrome.
How is resistance (R) calculated?
Calculate R from V/I for each length.
What is the formula for resistivity (p)?
p = RA / L
What is the relationship between resistivity and area?
1m = gradient x A
What is Ohm’s law?
V = IR
In a series circuit, how is the total potential difference (p.d.) distributed?
Total p.d. is shared between all components
What is the relationship of current in a series circuit?
Current is the same for all components
How is total resistance calculated in a series circuit?
Total resistance = sum of resistances
In a parallel circuit, what is the potential difference for each branch?
p.d. for each branch = p.d. of cell/battery
What happens to the total resistance when more resistors are added in parallel?
Adding more resistors in parallel REDUCES the total R
What does Kirchhoff’s 1st Law state?
Charge (and current) is conserved at any junction in a circuit (Itot in = Itot out)
What does Kirchhoff’s 2nd Law state?
The sum of EMFs (p.d. ‘rises’) must equal the sum of p.d. drops in a closed loop
Fill in the blank: In a parallel circuit, the total current is _______ among the branches.
split
If resistors are identical, how is the total voltage shared?
Total V must be shared equally
True or False: In a parallel circuit, the current flowing through each branch can be different.
True
What is the formula to calculate current (I) from voltage (V) and resistance (R)?
I = V/R
If the total voltage is 6V and the resistance in one branch is 30Ω with 0.2A flowing through it, what is the voltage across that branch?
V = IR = 0.2A * 30Ω = 6V
What is the behavior of an NTC thermistor when temperature increases?
Resistance decreases
NTC stands for Negative Temperature Coefficient, meaning resistance decreases as temperature increases.
What does a Light Dependent Resistor (LDR) do when light intensity increases?
Resistance decreases
An LDR operates similarly to an NTC thermistor but responds to light instead of temperature.
What is Ohm’s law?
V = IR
This formula relates voltage (V), current (I), and resistance (R).
How does the resistance of an NTC thermistor change with temperature?
If temperature increases, resistance decreases
This is the defining characteristic of NTC thermistors.
How does the resistance of an LDR change with light intensity?
If light intensity increases, resistance decreases
This allows LDRs to be used in light-sensing applications.
What happens to the voltage share in a potential divider circuit if the resistance of a thermistor decreases?
The thermistor gets a smaller share of the total voltage
This results in an increased voltmeter reading.
Fill in the blank: In a potential divider circuit, if light intensity decreases, the resistance of the LDR _______.
Increases
What effect does an increase in resistance of an LDR have on the voltmeter reading in a potential divider circuit?
Voltmeter reading increases
This is used to trigger devices like streetlamps.
In a circuit with a NTC thermistor, what occurs if the temperature decreases?
Resistance increases
This leads to a larger share of voltage going to the thermistor.
What is a practical application of a thermistor and an LDR in circuits?
Both can be used in potential divider circuits to detect changes in environment
This allows for automated responses to temperature and light changes.
What does EMF stand for?
Electromotive force
EMF is the energy supplied to each unit charge that passes through a battery.
What is the unit of EMF?
Volts (V) or Joules per Coulomb (J/C)
EMF is measured in volts, representing the potential energy per unit charge.
What does internal resistance (r) refer to in a battery?
The resistance within the battery that causes a voltage drop
Internal resistance affects the voltage available to the circuit.
What is terminal potential difference (V)?
The potential difference available to the circuit
It is measured by a voltmeter across the battery and does not include the voltage lost to internal resistance.
If the EMF is 6V and the terminal p.d. is 5.5V, how much voltage is lost due to internal resistance?
0.5V
This is the difference between the EMF and the terminal p.d.
What is the relationship between terminal p.d. (V), current (I), and internal resistance (r)?
V = IR
This equation shows how the terminal potential difference relates to current and internal resistance.
What is the formula that includes both EMF and internal resistance?
E = IR + Ir
This formula illustrates how EMF is divided between the load resistance and the internal resistance.
What does ‘load resistance’ refer to?
The resistance of the circuit
Load resistance is what the circuit uses to draw power from the battery.
True or False: The entire EMF is available to the circuit.
False
Some of the EMF is lost due to internal resistance, resulting in a lower terminal p.d.
Fill in the blank: The terminal p.d. is the p.d. _______ to the circuit.
available
The terminal p.d. represents the voltage that can be utilized by the circuit.
What happens when you use a variable resistor in a circuit?
It allows us to change the current
Adjusting the variable resistor modifies the load on the battery and affects the current flowing through the circuit.
What is the gradient of the terminal p.d. in relation to internal resistance?
-r
This indicates that as resistance increases, the terminal p.d. decreases.
how do we calculate number of electrons
number of electrons =total charge/magnitude of e(1.6*10^-19)
superconductivity
a material that has zero resistance and below critical temperature
Why is the filament I-V graph curved
The filament lamp is non-ohmic.As the current increases the frequency of collisions between electrons and the ions in a lattice increases,making them vibrate ,which causes the temperature to increase, making collisions even more likely ,which leads to resistance increasing
What happens to the flow of electrons when the emf increases and give an example for bonus points
The higher the emf = the faster the flow of electrons for example initially the emf is 6v and after the emf is 12 v the flow of electrons will increase by a factor of 2 or will travel twice as fast
