Electricity Flashcards
What is the unit of measurement for current?
Amperes (A)
Current is the rate of flow of charge in a circuit.
How is current (I) calculated?
I = Q/t
Where Q is charge in coulombs and t is time in seconds.
What is conventional current?
The rate of flow of positive charge
It flows in the opposite direction to the flow of electrons.
How is current conserved in a circuit?
Charge is always conserved
Current is conserved at a junction.
What instrument is used to measure current?
Ammeter
It is connected in series with the component.
What is potential difference (V) measured in?
Volts (V)
1 V = 1 J/C (joules per coulomb).
How is potential difference calculated?
V = E/Q
Where E is work done and Q is charge.
How is potential difference measured?
Voltmeter
It is placed in parallel across the component.
What is the relationship between potential difference and current?
V = IR
Higher potential difference results in greater current.
What is the unit of resistance?
Ohms (Ω)
Resistance is the difficulty for current to flow through a component.
How is resistance (R) calculated?
R = V/I
Where V is potential difference and I is current.
What characterizes an ohmic conductor?
Current is directly proportional to voltage
It has constant resistance.
What happens to resistance in a non-ohmic conductor like a filament lamp?
Resistance changes as voltage and current change
This is due to temperature effects on the material.
What is a thermistor?
A resistor whose resistance decreases as temperature increases
Used in temperature sensing applications.
What is a light dependent resistor (LDR)?
A resistor whose resistance decreases as light intensity increases
Commonly used in light-sensing circuits.
What are the characteristics of a series circuit?
Components are connected end to end in one loop
The same current flows through every component.
What is the relationship between potential difference and resistance in a series circuit?
The potential difference is shared across each component depending on their resistance.
The sum of the potential differences across the components is equal to the total potential difference across the supply. Components with a higher resistance have a greater potential difference across them.
How is total resistance calculated in a series circuit?
Total resistance is the sum of the resistances of each component: R = R1 + R2 + …
This indicates that the total resistance increases as more components are added in series.
Describe the configuration of components in a parallel circuit.
Components are connected to the power supply in separate branches.
Each branch allows current to flow independently.
What happens to the current in a parallel circuit?
The current is shared between each branch.
The sum of the currents in the separate branches is equal to the current through the source.
What is the potential difference across branches in a parallel circuit?
The potential difference is the same across every branch.
This uniformity makes parallel circuits advantageous for connecting multiple devices.
What is an advantage of connecting lamps in parallel?
If one lamp breaks, current can still pass through the rest.
This ensures that not all lamps go out if one fails.
List three hazards associated with electricity.
- Damaged insulation
- Overheating of cables
- Damp conditions
Each hazard poses a risk of electric shock or fire.
What role does a fuse play in an electrical circuit?
A fuse protects the circuit by melting if the current is too high.
Fuses have a current rating slightly higher than the device’s operating current, commonly 3A, 5A, and 13A.
How do circuit breakers differ from fuses?
Circuit breakers can be reset and operate faster than fuses.
They consist of an automatic electromagnet switch that breaks the circuit if the current exceeds a certain value.
What is the purpose of earth wires in electrical circuits?
Earth wires create a safe route for current to flow through in case of a short circuit.
This prevents electric shocks by directing excess current away from the user.
What is double insulation?
Appliances with double insulation have plastic casings or designs that prevent contact between the earth wire and the metal casing.
This design helps to prevent electric shocks.
What is the unit of energy measured in?
Joules (J)
What equation relates power, current, and voltage?
P = IV
How is energy transferred in a circuit?
From chemical energy in the battery to electrical energy used by circuit components and then to the surroundings
What is the formula for calculating energy transferred in a circuit?
E = IVt
What type of current flows in only one direction?
Direct current (d.c.)
What type of current continuously changes direction?
Alternating current (a.c.)
What is an example of alternating current?
Mains electricity
What is an example of direct current?
Current supplied by a cell or battery
Fill in the blank: The power of a component is measured in _______.
Watts (W)
What is the symbol for a diode?
Symbol for diode
What component is represented by the symbol for a battery of cells?
Battery of cells
What is the purpose of a transformer in a circuit?
To change the voltage level
What does an ammeter measure?
Current
What does a voltmeter measure?
Voltage
What is the function of a fuse or circuit breaker?
To protect the circuit from overload
What component is represented by the symbol for a lamp?
Lamp
What is the function of a thermistor?
Temperature sensing
Fill in the blank: A light-emitting diode is abbreviated as _______.
LED
True or False: A microphone is used to convert sound into electrical signals.
True
What is the function of a motor in a circuit?
To convert electrical energy into mechanical energy
Fill in the blank: A variable resistor is also known as a _______.
Rheostat
What does a light-dependent resistor (LDR) do?
Changes resistance based on light intensity
What is the role of a loudspeaker in an electrical circuit?
To convert electrical signals into sound
What is the unit of measurement for electric charge?
Coulombs (C)
What are the two types of electric charges?
Positive and negative
What happens to opposite charges and like charges?
Opposite charges attract and like charges repel
What subatomic particles make up an atom and their charges?
- Protons: +1 charge
- Electrons: -1 charge
- Neutrons: 0 charge
What does charging a body involve?
The addition or removal of electrons
What do charged atoms create?
Ions
What are conductors and insulators?
- Conductors: Allow electrons to flow
- Insulators: Impede the flow of electrons
What occurs when two insulators are rubbed together?
Electrons move from one to the other, leading to charging
What happens to the materials when one loses electrons and the other gains?
- Material losing electrons: Positively charged
- Material gaining electrons: Negatively charged
What builds up when charges cannot move within an insulator?
Static electricity
What is a phenomenon caused by static electricity?
Lightning
How does electrostatic charge build up on clouds?
Due to friction
What happens when the electrostatic charge on clouds becomes large enough?
Clouds discharge through the air to the earth, resulting in lightning
Why does a positively charged balloon stick to a wall?
Positive charges in the wall are repelled, leaving a negative charge on the wall
What effect does rubbing a comb against an insulator have?
It causes the comb to pick up an electrostatic charge
What happens to bits of paper when a charged comb is brought near?
The paper closest to the comb becomes oppositely charged and is attracted to it
What are some dangers of electrostatic charges?
- Risk of electric shock
- Sparks igniting fuel during aircraft and tanker refueling
What is earthing?
Providing electrons an alternative pathway to the earth
Fill in the blank: Charging a body involves the addition or removal of _______.
Electrons
True or False: Static electricity can cause sparks that may ignite fuel.
True
What does reducing electrostatic charge on an insulator prevent?
It prevents too much electrostatic charge from building up, reducing the risk of electric shock.
What is one use of electrostatic charges in inkjet printers?
Droplets of ink are charged and pass between two charged metal plates, one positive and one negative, to direct them towards the paper.
In an inkjet printer, how are ink droplets manipulated?
They are attracted to the plate with the opposite charge and repelled by the plate with the same charge.
How does a photocopier utilize electrostatic charges?
It projects an image onto a positively charged plate where light falls, causing the charge to leak away, attracting negatively charged toner particles to the positive areas.
Fill in the blank: In a photocopier, paper is placed over the plate to transfer _______.
[toner]
True or False: In a photocopier, positively charged toner particles are attracted to positively charged areas.
False
