aca dec sci-91 sec 3

What does the magnetic field created by the solenoid do?

The magnetic field created by the solenoid will be whatever it needs to be to oppose the external change.

What does the solenoid's opposing magnetic field create?

This creates a sort of resisting force for the process, which means that to keep the current going requires constant input.

Why can't this process continue indefinitely without energy input?

This prevents this process from continuing indefinitely without external energy input; in other words, this prevents the use of a generator as a perpetual motion machine.

What is the voltage across power lines compared to the voltage of a home outlet?

The voltage across power lines can be many thousands of volts, but the voltage of the electrical outlet in your wall is only 120 V.

How can voltage be stepped down to safe levels?

The voltage can be stepped down to safe levels via something called a transformer.

What are the two coils in a transformer called?

Coil 1 is the primary coil, and coil 2 is the secondary coil.

What happens when coil 1 is connected to a power source?

Coil 1 will have current running through it, and therefore coil 1 will also generate a magnetic field around it.

What happens if the current in coil 1 is steady?

As long as the current remains steady, then the magnetic field will also be steady, and therefore nothing happens with coil 2.

How do we induce a voltage in coil 2?

Since we need a changing magnetic field to induce a voltage in coil 2, we need a changing current in coil 1.

What type of current in coil 1 generates a changing magnetic field?

If we make our current an alternating current (AC), then the current is constantly switching directions, and so the magnetic field it creates is also switching directions, which will induce a voltage in coil 2.

How does the voltage induced in coil 2 relate to the number of loops?

The amount of voltage induced depends on the number of loops in our coil.

What equation relates voltage and number of loops in a transformer?

V1/N1 = V2/N2

What happens if N2 is bigger than N1?

If N2 is bigger, V2 must also be bigger.

Why does increasing the number of loops affect current?

If N2 is bigger than N1, and therefore V2 is bigger than V1, then the current in coil 2 actually ends up being less than the current in coil 1 due to the increase in resistance.

Why is it beneficial that current decreases when voltage increases?

This is beneficial because high voltage across many miles of wire would be dangerous; stepping down voltage makes it safe for home use.

What do the cylindrical tubes at the top of power poles represent?

They are transformers used to decrease the voltage to safe levels before the current enters a home (Figure 82).

How is power drawn from a circuit expressed?

Power drawn from a circuit can be written as P = IV.

Why do we want high voltage and low current in power lines?

High voltage with low current gives a decent amount of power while reducing energy lost as waste heat in long wires.

How can a capacitor smooth out AC in a circuit?

A capacitor charges when the current goes one way and discharges when the current goes the other way, creating something approximating a constant DC flow.

What is the purpose of a diode in AC circuits?

A diode allows current to flow through it only in one direction.

What is an inductor?

An inductor is a solenoid attached to the circuit on either end that resists changes in current.

How does an inductor resist changes in current?

An inductor creates its own current and magnetic field to oppose any changes in the surrounding magnetic field (Lenz's law).

What happens when you close a switch in a circuit with an inductor?

The current gradually climbs to its maximum value, resisted by the inductor.

What happens if the circuit is broken with an inductor present?

The inductor will resist the change and try to keep the current going, sometimes causing a spark (self-induction).

What components can we connect to a power source in a basic circuit?

A resistor, a capacitor, and an inductor.

What happens when a charged capacitor is connected to an inductor?

The capacitor starts to discharge, current flows through the inductor, and the inductor resists the decrease in current, creating a counter-current.

How does the capacitor-inductor circuit behave over time?

The counter-current keeps going even after the capacitor discharges, charging it in the opposite orientation, and the cycle continues back and forth, like a pendulum.

What is this back-and-forth current in the capacitor-inductor circuit analogous to?

It is analogous to the swing of a pendulum.

What is the frequency at which the capacitor-inductor circuit oscillates?

f = 1 / 2π√LC

What do C and L represent in the resonant frequency equation?

C is the capacitance of the capacitor, and L is the inductance of the inductor.

What is another name for the resonant frequency?

This frequency is sometimes referred to as the natural or resonant frequency.

What is resonance?

Resonance is a property of oscillating systems where a system oscillates with greater magnitude when driven at its natural frequency.

What is an example of resonance with a pendulum?

A child on a swing swings at the same natural frequency regardless of height; pushing at the same frequency increases swing amplitude.

How can resonance cause damage in everyday objects?

If a driving force matches the natural frequency of an object, such as a singer hitting a note that matches a wine glass's resonant frequency, the object can vibrate so much that it breaks.

How does an AC-connected capacitor-inductor circuit behave at resonant frequency?

If connected to an AC source that matches the circuit's resonant frequency, maximum current occurs.

How can we change the resonant frequency of a circuit?

We can change the resonant frequency by changing the capacitance or inductance of the circuit.

How does tuning a radio relate to resonance?

Tuning a radio changes the capacitor plates to adjust the resonance of the circuit to receive specific signals.

Who invented the lightbulb?

This is complicated; Thomas Edison is often credited, but he was the first to mass market it.

Who actually invented the first electric light?

The first electric light was invented in 1705 by Frank Hauksbee.

What was Hauksbee's "barometric light"?

It was a mercury barometer which, when shaken, caused the mercury to shed electrons onto the interior of the glass container, ionizing the gas inside and creating light.

What was the first electric light to see widespread use?

The first electric light to see widespread use was the arc lamp, which was invented by Humphrey Davy around 1802-09.

How does an arc lamp work?

An arc lamp creates a large enough voltage between two pieces of metal to result in dielectric breakdown, thereby generating a miniature lightning bolt.

Why does the arc lamp air continue to glow?

However, the voltage is maintained, so the air continues to glow rather than merely flash.

When did many cities begin to use arc lamps?

The process of building arc lamps was refined over time, and by the 1860s, many cities were lit up with arc lamps.

What was the limitation of arc lamps?

Arc lamps had limited use, however, as they did not last very long.

How do incandescent lights produce light?

Incandescent lights emit light by causing a solid object to heat up enough so that it glows.

Who invented incandescent lights?

Incandescent lights were invented by multiple people around the same time, but Thomas Edison was the first to not just create a bulb, but to build an entire infrastructure around powering them in cities.

When did Edison light up part of New York City?

In 1882, Edison lit up part of New York City with his direct current lightbulbs.

Who promoted alternating current and lit up a town?

George Westinghouse founded his own electric company, and a few years later, Westinghouse lit up a town with alternating current.

What feud began between Edison and Westinghouse?

The infamous feud between Edison and Westinghouse began over DC vs AC electricity.

Why was Edison concerned about AC?

Edison was concerned about the dangers of AC, fearing that high voltages causing electrocutions could dissuade people from electricity entirely.

What propaganda campaign did Edison initiate?

Edison began a propaganda campaign to try to prove to the public the supposed dangers of AC, culminating in the first execution of a prisoner via the electric chair (powered by AC).

What paradox existed with Edison and the death penalty?

Edison had expressed opposition to the death penalty, but he felt this act was justified to create a negative association specifically with AC.

Who invented the three-phase generator in 1891?

Mikhail Dolivo-Dobrovolsky invented a three-phase generator in 1891.

Why was the three-phase generator important?

It allowed an efficient transfer of current over long distances using AC, adopted by Westinghouse.

Who created the tungsten lightbulb in 1904?

Alexander Just and Franjo Hanaman created the tungsten lightbulb.

Why was the tungsten lightbulb significant?

The tungsten lightbulb was more efficient and longer lasting than the carbon ones Edison made and eventually became the international standard.

Why is Edison still associated with the lightbulb?

Edison was a brilliant inventor, but he was even more brilliant at marketing, which is likely why even today he is still associated with the lightbulb.

How was Nikola Tesla portrayed in relation to Edison?

Tesla has often been portrayed as Edison's chief rival, with Edison usually cast as the villain.

Did Tesla actually work for Edison?

Tesla worked for Edison's electric company in his early career and initially spoke kindly of Edison.

What is Tesla's contribution to AC infrastructure?

Tesla patented many inventions, some of which ended up being useful in building AC infrastructure.

How did Tesla exaggerate his contributions?

Tesla talked himself up and claimed credit for many things he did not create, later ranting about supposed inventions and fantasies of infinite energy and communicating with Martians.

What did Tesla actually invent?

Tesla invented real things, including the Tesla coil, first demonstrated in 1891.

What does a Tesla coil do?

The Tesla coil creates a high voltage on a metal ball on top of a coil of wire, enough to shoot lightning bolts into the air.

Does a Tesla coil serve a practical purpose?

A Tesla coil does not do anything beyond creating cool lightning effects, but it inspires people to get into science.

What are the two types of magnetic "charge"?

Magnetism has two types of charge, called north and south instead of positive and negative.

How do magnetic poles interact?

Two north poles and two south poles repel, and a north and south pole attract one another.

Do individual electrons have magnetic poles?

Even individual electrons have both a north and south pole.

What surrounds magnets like electric charges?

Magnets have a magnetic field around them, similar to electric fields around charged particles.

What is indicated by a magnetic field?

The magnetic field indicates the way a compass will point.

Where do magnetic fields come from?

Magnetic fields come from moving electric charges.

What magnetic field does a current-carrying wire have?

A wire with an electric current has a magnetic field around it.

Do atoms have magnetic fields?

The motion of charged particles within atoms creates magnetic fields, making every atom a magnet.

Are atomic magnetic fields always aligned?

In most objects, the magnetic fields of individual atoms point in different directions.

What happens in magnetic objects?

In magnetic objects, all the individual atomic magnets are aligned.

Can objects be temporarily magnetized?

Certain objects can have their atoms temporarily magnetized when exposed to a strong magnetic field.

What creates the Earth's magnetic field?

The core of the Earth is believed to be a giant ball of molten iron, creating a planet-wide magnetic field.

Where does a compass point in terms of magnetism?

The north end of a compass points toward the Arctic pole, which is actually the Earth's magnetic south pole.

How does the Earth's magnetic field protect us?

The Earth's magnetic field deflects potentially harmful particles from outer space, creating the aurora at the poles.

What rule helps visualize magnetic force vectors?

The magnetic force follows the right-hand rule, helping visualize force, velocity, and magnetic field vectors in perpendicular directions.

Does magnetic force change particle speed?

The force of the magnetic field does not speed up or slow down particles but deflects them.

What is a solenoid?

A solenoid is multiple loops of wire wrapped on top of each other, creating a cylinder of one continuous loop of wire.

What magnetic field does a solenoid create?

When current runs through a solenoid, it creates a magnetic field similar to that of a bar magnet, with one end being a north pole and the other a south pole.

How can a changing magnetic field generate electricity?

A changing magnetic field can accelerate charged particles from rest and create an electric current in a wire.

What types of motion create a changing magnetic field?

The changing magnetic field can come from either the wire moving near the magnet or the magnet moving near the wire.

How does a solenoid react to a nearby magnet?

A solenoid will become a magnet if it is moved near another magnet, and its magnetic field will line itself up to oppose the change.

What happens if a magnet moves toward a solenoid?

The solenoid will repel it.

What happens if a magnet moves away from a solenoid?

The solenoid will attract it.

How do power plants generate electricity?

Power plants generate power by rotating a loop of wire near a strong magnet, often using steam to rotate the wire.

How can one coil induce voltage in another coil?

One coil can induce a voltage in another nearby coil via the alternating magnetic field it creates.

What type of current is required for coil induction?

Only alternating current, which creates a constantly changing magnetic field, works to induce voltage in a nearby coil.

What does an inductor do in a circuit?

An inductor resists any changes of current, allowing current to increase or decrease gradually.

What happens when an inductor is combined with a capacitor?

An inductor combined with a capacitor will cause current to switch directions back and forth at a certain frequency.

Did Thomas Edison invent the first lightbulb?

Thomas Edison did not invent the first lightbulb, but he was one of the pioneers of spreading electricity to multiple buildings.

Why did Edison support DC initially?

Edison initially supported the use of DC, thinking AC's higher voltages would be too dangerous for home use and unaware of transformers mitigating the danger.

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