4A3 Electrical Current and Capacitance Flashcards
Describe the properties and types of electrical current, and explain the role of capacitance. (60 cards)
Define:
Electric current
The flow of electric charge through a conductor per unit time.
Measured in amperes (A); 1 A = 1 coulomb/second.
How does potential difference affect current in a circuit?
The potential difference drives the current through a circuit.
Also called voltage, it is measured in volts (V).
How is electrical current created?
It is caused by electrons moving through a conductor due to an applied voltage.
The movement is driven by the electric field established by the voltage source.
What is the SI unit of electric current?
Ampere (A)
It is equivalent to Coulomb/second (C/s), where Coulomb (C) is the SI unit of charge.
True or false:
Resistance is the opposition to the flow of electrical current.
True
Resistance is measured in ohms (Ω).
Fill in the blank:
Electrical resistance is affected by the material’s _______ and its temperature.
resistivity
Resistivity quantifies how strongly a material opposes current flow.
Why do metals like copper have low resistance?
Metals have a high number of free electrons that can move easily under an electric field.
This makes them excellent electrical conductors.
What does resistivity measure?
It measures how strongly a material opposes the flow of electric current.
It is measured in ohm-meters (Ω·m).
How does the length of a conductor affect its resistance?
The longer the conductor, the higher its resistance.
Longer conductors provide more material for electrons to collide with.
How is the resistance of a circuit measured?
Using an ohmmeter.
To make the measure, the circuit must be de-energized to avoid inaccurate readings or damage to the device.
Fill in the blank:
The instrument used to measure electrical current is called a(n) _______.
Ammeter
An ammeter is connected in series with the circuit to measure the current flowing through it.
What is the difference between a galvanometer and an ammeter?
Both devices detect electric current, but an ammeter measures its magnitude, while a galvanometer determines the direction and strength of small currents.
Galvanometers are often converted into ammeters by adding a low-resistance shunt.
Define:
Potential difference
Difference in the amount of energy that charge carriers have between two points in a circuit.
It is measured in volts (V)
How is the voltage measured?
It is measured using a voltmeter connected in parallel with the component or circuit.
It is important to ensure that the range setting of the voltmeter matches the expected voltage for accurate measurements.
What does Ohm’s Law state?
Current (I) is directly proportional to voltage (V) and inversely proportional to resistance (R).
Formula: V=I×R
What is the formula to calculate current using Ohm’s Law?
I= V/R
Current is measured in amperes (A).
True or false:
If resistance increases while voltage remains constant, current will increase.
False
Current decreases when resistance increases at constant voltage.
Explain why Ohm’s Law is important in circuit design.
It helps determine the correct resistance values to ensure safe current flow and voltage distribution in circuits.
Essential for power regulation and safety.
For which types of circuits does Ohm’s Law apply?
It applies to linear circuits where the resistance remains constant regardless of the voltage or current.
These circuits are typically made of ohmic materials, such as metals under normal conditions. Non-linear components, like diodes and transistors, do not follow Ohm’s Law as their resistance changes with voltage and current.
Define:
Non-ohmic material
Material in which the resistance does not remain constant and does not follow Ohm’s Law.
In these materials, the current-voltage relationship is non-linear. Examples of non-ohmic materials include semiconductors, diodes, and transistors.
If a circuit has a voltage of 12V and a resistance of 4Ω, what is the current?
3A
I = V / R = 12V / 4Ω = 3A
What happens to current if both voltage and resistance double?
The current remains unchanged.
Doubling both voltage and resistance keeps their ratio constant.
How does temperature affect the applicability of Ohm’s Law?
Rising temperatures can make materials non-ohmic by altering their resistance.
Filament lamps deviate from Ohm’s Law when heated.
A resistor has 0.5 A of current and 5 V across it. What is its resistance?
10Ω
R = V / I = 5 V / 0.5 A = 10 Ω