Electricity Chapter Fundamentals

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Questions and Answers

What is the relationship between potential difference (p.d.) and the rate at which energy is transferred?

p.d. influences energy transfer only in resistive components.

Higher p.d. results in more energy being transferred per unit charge. (correct)

Lower p.d. leads to a faster transfer of energy.

p.d. does not affect energy transfer in a circuit.

What is the main purpose of an ammeter in a circuit?

To control the flow of current in the circuit

To measure voltage across components

To measure the potential difference

To measure the current flowing through the circuit (correct)

What does the term 'electromotive force' (e.m.f.) refer to?

The total charge in a circuit

The work done by a source in moving a unit charge around a complete circuit (correct)

The voltage across a battery at rest

The resistance encountered by electrons in a circuit

How is the electromotive force (e.m.f.) of a supply defined?

As the energy transferred per coulomb when charge moves around a circuit. Signup and view all the answers

When measuring potential difference with a voltmeter, where should the voltmeter be connected?

Parallel with the component across which p.d. is to be measured. Signup and view all the answers

How does the direction of flow in alternating current (a.c.) differ from that of direct current (d.c.)?

A.c. flows back and forth, while d.c. flows in a single direction Signup and view all the answers

Which of the following equations correctly relates work done, charge, and potential difference?

W = Q × V Signup and view all the answers

What is the unit of frequency in an alternating current?

Hz (hertz) Signup and view all the answers

What happens to the pointer of an ammeter when measuring alternating current at a slow frequency?

It fluctuates around zero Signup and view all the answers

What happens to the energy transferred by a circuit when the e.m.f. is increased?

The energy transferred increases for each coulomb. Signup and view all the answers

In a circuit, which statement about Mr. Coulomb is accurate?

Each Mr. Coulomb carries a bundle of energy and releases it at each component. Signup and view all the answers

Which of the following statements best describes potential difference (p.d.)?

It is the work done by a unit of charge passing through a component Signup and view all the answers

What occurs at the terminals of a battery that enables it to maintain a flow of current?

A surplus of electrons at the negative terminal Signup and view all the answers

What is indicated by the term 'voltage' in electrical terminology?

Voltage can be used interchangeably with potential difference measured in volts. Signup and view all the answers

What defines the frequency of an alternating current if it has a frequency of 2 Hz?

There are two cycles per second Signup and view all the answers

How does the potential difference across a lamp affect its performance?

Increased potential difference results in more light and heat output. Signup and view all the answers

What happens to the current in a circuit when a variable resistor is adjusted to reduce resistance?

The current increases. Signup and view all the answers

Which material is commonly used to make fixed resistors?

Carbon. Signup and view all the answers

In an electrical measurement, if the expected voltage exceeds the selected range, what should be done?

Increase the range to a higher one. Signup and view all the answers

What is defined as the opposition of a conductor to current?

Resistance. Signup and view all the answers

Which type of resistor is specifically designed to change the potential difference in a circuit?

Potentiometer. Signup and view all the answers

How is resistance typically expressed in terms of its values?

In ohms, ranging from one to millions of ohms. Signup and view all the answers

What alloy composition is used for making variable resistors or rheostats?

60% copper and 40% nickel. Signup and view all the answers

What describes the electromotive force (e.m.f) in a circuit?

Potential difference generated by a source. Signup and view all the answers

Study Notes

Electricity and Magnetism

Electricity and magnetism are interrelated phenomena.
An atom is composed of a nucleus with positively charged protons and uncharged neutrons, surrounded by negatively charged electrons.
The charges on protons and electrons are equal and opposite.
Like charges repel, unlike charges attract.
Static electricity is the buildup of electric charge on the surface of objects.
Charge transfer occurs when electrons move between materials when rubbed together.
The unit of charge is the coulomb (C).
The charge of an electron is 1.6 x 10^-19 C.
A gold-leaf electroscope is used to detect electric charge and its polarity.
Conductors allow charges to move freely.
Insulators resist the flow of charges.
Examples of conductors include metals.
Examples of insulators are plastics and rubber.

Electrical Quantities

Electric current is the rate of flow of electric charge.
The unit of current is the ampere (A).
Current is measured in amperes (A), where 1 A = 1 C/s.
The current flowing through a circuit is a measure of how much charge passes a given point in the circuit per unit time.
The relationship between charge, current and time is given by the equation I = Q/t
Ohm's law states that current (I) is directly proportional to the potential difference (V) and inversely proportional to the resistance (R).
The equation is V = IR
Resistance (R) is the opposition to the flow of current in a circuit / component.
The unit of resistance is the ohm (Ω)
An ammeter is a device used to measure current in a circuit.
A Voltmeter is a device used to measure voltage.

Electric Current

Electric circuit current consists of moving charges.
In a direct current (dc) the charges flow in one direction.
In an alternating current (ac), the direction of the current flow reverses regularly.
The frequency of an alternating current (a.c) is a measure of how many times the current switches direction each second measured in Hertz (Hz).
The definitions of an ampere and a coulomb refer to the amount of electric charge that passes in a given time.

Electromotive Force and Potential Difference

Electromotive force (emf) is the electrical work done by a source in moving a unit charge around a complete circuit, measured in volts
Potential difference (pd) is the work done by a unit charge passing through a component, measured in Volts.
The unit of both emf and potential difference (voltage) is the volt.
The similarity between emf and pd is that they are both related to the amount of energy per unit of charge

Energy Transfer and pd

Potential difference controls how quickly electrical energy is transferred in a circuit.
Voltage is the rate at which electrical energy is converted in a circuit.
Potential difference (p.d) is a measure of energy transfer.
The unit of electrical power is the watt (W).
Electrical power is the rate of transfer of energy in a circuit.
Electrical energy = Power x time.

Resistance of a Metal Wire

Resistance of a metal wire depends on its length and cross-sectional area.
The resistance increases when the length is increased.
The resistance decreases when the cross-sectional area increases.
The resistance also depends on the material.
the equation for resistivity in terms of resistance, length, cross-sectional area is R= ρl/A

Resistors

Resistors reduce the current flowing through the circuit / component.
Resistors are used in various circuit designs to control current flow.
A variable resistor is called a rheostat.
A variable resister is called a potentiometer.

I-V graphs

The variation of current with voltage in different types of conductors.
Ohm's law applies to the behaviour of ohmic conductors.
In an ohmic conductor, current is linearly proportional to voltage.
Filament lamps do not obey Ohm's law because resistance increases as current / temperature increases.
A thermistor's resistance decreases when the temperature increases.

Electrical Safety

Electric shock happens when electricity flows through your body.
The current takes a path through your body to cause shock.
Wet conditions cause worse shocks because water reduces the resistance to current flow.
Rubber-soled shoes, and/or standing on a dry surface increase resistance and help protect against electrical shock.
Fuses protect circuits from excessive current by melting.
Trip switches (circuit breakers) protect circuits from excessive current using an electromagnet to switch circuits off quickly.
RCDs (residual current devices) detect differences in current between live and neutral wires to quickly switch off circuits.
Electrical components should be correctly connected to the earth wiring.
Double insulation protects components by using extra insulation to protect from unwanted shorts.

Magnetic Poles

Magnetic forces are strongest at magnetic poles.
Magnetic poles always occur in pairs; north(and south)
Like magnetic poles repel; opposite attracts.
The strength of magnetic fields is greatest near the poles.
Magnets can be used as compasses.

Induced Magnetism

A magnetic material becomes magnetised when it comes into contact with a permanent magnet;
Temporary magnets are easily magnetised and demagnetised (e.g., iron).
Permanent magnets are difficult to magnetize but retain their magnetism once magnetized (e.g., steel).

Magnetic Fields

A magnetic field surrounds a magnet.
Lines of force indicate the direction of the magnetic field.
The strength of a magnetic field is greater where the lines of force are close together.

Electromagnets

An electromagnet involves the use of an electric current in a coil to create a magnet.
The strength of an electromagnet is proportional to the current and the number of turns of the coil.

Electromagnetic Induction

When a wire moves through a magnetic field, or when a magnetic field changes around a wire, a current is induced in the wire.
This is electromagnetic induction.
The induced current has a direction that opposes the change that created it.
The amount of induced current depends on the rate of change of the magnetic field.

D.C. Motors

The motor effect relates the movement of a wire in a magnetic field to a current flow.
Practical motors have coils of wire wound around a soft iron core.
Increasing the number of turns of wire on the coil or the current flowing through the coil increases the turning effect/torque of the motor.

Moving-Coil Galvanometers

A galvanometer is a device used to measure small electric currents.
A moving-coil galvanometer contains a coil of wire that rotates in a magnetic field.
The rotation of the coil is proportional to the current flowing through the coil.
The direction of the coil's movement depends on the direction of the current.

Paying for Electricity

Electricity energy is measured in kilowatt-hours (kWh).
The kilowatt-hour (kWh) is the amount of energy consumed by a 1kW appliance in one hour.
Electrical energy is calculated using the equation: Electrical Energy (kWh) = Power (kW) x Time (hours).
Energy providers charge for the energy used which is measured in kilowatt hours.

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Description

This quiz tests your understanding of key concepts in electricity, including potential difference, electromotive force, and the functions of ammeters and voltmeters. Answer questions about current types and their characteristics to gauge your knowledge of electrical principles.