5.1 Current Electricity Flashcards
What’s current and it’s units
Rate of flow of charge
Amperes (Amps)
What’s potential difference
Work done moving a unit charge between 2 points in a circuit
What’s resistance
How difficult it is for current to flow through a component
Component has resistance of 1 Ohm if 1A flows through it when a P.D of 1V is applied across it
What’s ohmic conductor
Obeys Ohms Law
Current is directly proportional to potential difference as temperature is constant
How do you measure the current
Ammeter in series to test component
How do you measure potential difference
Voltmeter in parallel to test component
What does the gradient of a I-V graph represent
Rate of change of current with correlation to voltage
How does a Ohmic conductor graph look like
Line has a constant gradient and passes through origin, showing that voltage is directly proportional to current
How does an I-V graph represent a component with a higher resistance
A steeper line = resistor has low resistance
A shallow line = resistor has high resistance
What’s the name of the component that has a curve gradient passing through origin
Filament lamp
As current increases the resistance also increases
Greater increase in voltage produces only a low increase in current
Why does the current increasing on a filament lamp cause an increase in resistance
Electrons flowing in wire start to collide with metallic ions within metallic lattice structure more often
Since it affects flow of electrons as that attempt to flow through conductor and effective resistance will increase
What’s a diode
Allows current to flow through one direction
Unless stated in question, should you assume that voltmeters to have zero resistance or infinite resistance
Assume infinite resistance
Current takes path of least resistance so voltmeter has infinite resistance when applied in parallel to component no current will flow through it and all current will flow through appliance
Should you assume that an ammeter has zero resistance unless stated otherwise
Means that there would be 0 P.D across ammeter and no energy is lost across it; doesn’t affect circuit
What’s LDR
Semiconductor that’s sensitive to light
As light intensity increases, resistance decreases
How does thermistor work
As temperature increases, resistance decreases
Means thermistors have a negative temperature coefficient
What’s resistivity
Resistance of a 1m cylinder with a cross sectional strap of 1m^2
Resistivity is an inherent property of a material
Describe an experiment to determine resistivity of a metal
- Measure diameter of wire with micrometer and calculate cross sectional area = π(d/2)^2
- Set up circuit
- Vary wire length and record voltage and current for each length
- Use R=V/I to work out resistance
- Plot graph of resistance against wire length
- Gradient =
resistivity / cross sectional area - So resistivity =
gradient x cross sectional area
What’s a superconductor
Material that has a resistivity of 0 at or below critical temperature
Critical temperature is an inherent property of material
How do you find total resistance in a series circuit
Rtotal = R1 + R2
Add individual resistance of each component
If 6 cells, each 5V, are arranged in series what voltage is provided to circuit
30V = 5V x 6
How does current vary between each component of a series circuit
Current is same through all components so it does not vary
Is current same in parallel components
No, each branch of a parallel circuit can have different currents through them according to Kirchhoff’s first Law
What is Kirchhoff’s first Law
All current going into a junction is equal to current leaving junction
