SCI 1010 TEST 4

What is a galvanometer?

galvanometer uses a movable coil of wire placed in a magnet

Explain magnetic domain

groups of atoms with aligned magnetic poles

A step-up transformer in an electrical circuit increases _________.

voltage

A step-down transformer in an electrical circuit decreases ___________ and increases __________.

voltage; current

Explain magnetic fields

- The magnetic field, a vector, is the state of space around a magnet. - Unlike electric fields, magnetic fields have no start and end points. - They exist as completely closed loops. They are present inside and outside of the magnet. - produced by the motion of electric charge

Explain magnets

- The ends of a magnet are called its poles. - A north pole and a south pole. - Magnets are dipoles. - That is, there are always two poles. - Opposite poles attract one another. Like poles repel one another.

What is an ion? What does it mean for an ion to be positively/negatively charged?

- An atom with an excess positive/negative charge is called an ion. - Ions arise when electrons are exchanged between atoms. - If electrons are added to a neutral atom, the ion formed has a net negative charge. - If electrons are removed from a neutral atom, the ion formed has a net positive charge.

Define circuit. Define the two types

- Any path along which electrons can flow is a circuit. - For a continuous flow of electrons, there must be a complete circuit with no gaps. That is, the circuit must be closed. - Devices are commonly connected in a circuit in one of two ways: in series or in parallel. - series: current through each component is the same/ the voltage is different/ one goes out, so do the rest (christmas lights) - parallel: the current across each component will be different/ voltage will be the same (all connected independently to battery, if one goes out they all dont

Explain the two types of currents

- Direct current (DC) is current that only points in one direction. - The charges in DC have a net motion from the negative terminal to the positive terminal. - A battery is an example of a DC source. - Alternating current (AC) is current that changes direction with a set frequency (60 cycles per second in the U.S.). - Thus, the charges do not have a net motion, but simply wiggle back-and-forth. - The outlets in your home use AC.

Explain electric field

- Electric charge is the property responsible for the electric field. - Now, keep in mind that the charge does not create, generate, or produce a field. The field simply exists because the charge exists. - Electric fields interact to give rise to the electrostatic force that we've discussed.

Define semi conductors. Give examples.

- Some materials, such as germanium or silicon, can be made with either an excess or a deficiency of conducting electrons/ making them versatile to conductors or insulators

What is action at a distance?

- The concept of forces being exerted over a distance instead of through contact

What is a transformer? Name two types

- When changes in the magnetic field of one coil of wire are intercepted by another coil, a voltage (and therefore a current) is induced in the second coil. - contains two coils not connected - the one near the input is the primary, near output is secondary - A transformer has the ability to increase (step up) or decrease (step down) an input voltage. - step up: increases voltage, decreases current - step down: decreases voltage, increases current - more loops on secondary, step up, fewer loops on secondary, step down

What is resistance? What is the unit?

- an impedance to an electric current - Ohms - The resistance in an electrical system is directly proportional to: The length of the system. The temperature of the system. The type of material (measured by a property called resistivity). - It is inversely proportional to the radius of the system squared. That is, a thinner wire has a higher resistance than a thicker wire.

What charge does electric fields begin/end on? What do electric fields point towards/away from?

- electric fields "begin" on positive and "end" on negative. - point away from positive, towards negative

What is the elementary charge in Coulombs? The charge of an electron/proton/neutron?

- elementary: 1.602 x 10^-19 C - electron: -1.602 x 10^-19 C - proton: + 1.602 x 10^-19 C - neutron: 0 C

How is everything not magnetized? Name examples of easily magnetized matierals

- every electron is like a tiny spinning magnet, but if they spin in opposite directions then it cancels out - materials like nickel, iron and cobalt are ferromagnetic or easily magnetized

Explain electric power. what is the unit

- moving electric currents do work - so power is the product of current and work - measured in watts (W)

Explain the two parts of the atom

- nucleus- The nucleus is in the center of the atom. It contains the protons and neutrons of the atom. Therefore, the nucleus has a net positive charge - electron cloud- contains the electrons of the atom. The electrons are negatively charged

What does it mean for an atom to be neutral?

- protons and electrons are equal

What is a force field?

- the altered state of space around an object caused by some property of the object - The mere presence of an object affects dimensional space around it. - Different properties will affect the space differently. - These regions of affected space are force fields.

What is electric potential? What is its unit?

- the electric potential energy of a system per change - electric potential energy divided by charge - unit of volts (V) referred to as voltage

Explain potential difference

- when the ends of an electric conductor are at different electric potentials - i.e., when there is a potential difference - charges in the conductor flow from the higher potential to the lower potential. - Without a potential difference, - i.e., a voltage - no flow of charge occurs. - Devices that provide this potential difference are often called voltage sources. e.g., batteries, power supplies, outlets, etc.

In a circuit consisting of two lamps connected in series, if the current in one lamp is 1 A (1 amp), what is the current in the other lamp?

1 A

Compare a generator and an electric motor.

A generator converts mechanical energy into electrical energy. A motor converts electrical energy into mechanical energy

How does the charge of one electron compare with that of any other electron?

All electrons have the same charge

Why is iron magnetic and wood not magnetic?

Atoms in wood do not organize into domains like iron atoms do

How do you induce a voltage in a conducting loop of wire?

Change the magnetic field in the loop.

What is meant by saying that charge is conserved?

Charge cannot be created or destroyed, only transferred

What is the unit for electric charge?

Coulomb (C)

Define current. What is the unit. What is a common misconception of it

Flow of charges/ amount of charges that passes a point in some amount of time - unit is ampere (amps) (A) - misconception: moves at the speed of light, actually moves rather slow

What important discovery did Michael Farady and Joseph Henry make?

Electromagnetic induction

How can you make an object polarized?

If the charges cannot move from relatively stationary positions, then bringing a charged object close to them will cause them to become electrically polarized

Distinguish between DC and AC.

In DC, charges "flow" in one direction. In AC, charges alternate direction

It is possible to melt metal with a rapidly-changing magnetic field. What is actually causing the metal's temperature to increase?

The current induced by the changing magnetic field

What important connection did Maxwell discover between electric and magnetic fields?

Light is made of a combination of oscillating electric and magnetic fields

What is the unit of electrical resistance?

Ohm

What was the amber effect?

The Greeks found that rubbing amber (fossilized tree sap) with fur of some sort would cause the amber to attract light objects, like feathers

The circuit within an incandescent bulb is shown below. Which of the battery arrangements will light the bulb?

The bulb connected to the battery with one side connected to the end of the bulb and one side connected to the metal ring

What is the shape of a magnetic field about a current-carrying wire?

The field is composed of concentric circles centered on the wire

What is Coulomb's Law?

The force exerted between two electrostatic charges is - directly proportional to the product of the charge magnitude - inversely proportional to the square of the distance between the charges (decreases with distance)

A changing electric field in free space (e.g., a vacuum) induces

a changing magnetic field

Which part of an atom is positively charged? Which part is negatively charged?

The nucleus is positively charged. The electrons are negatively charged.

How does the number of electrons in a neutral atom compare to the number of protons?

There are as many electrons as there are protons

Explain superconductors

Under normal conditions, all conductors exhibit electrical resistance. This resistance is temperature-dependent. There exists a temperature for materials (called the critical temperature) at which the electrical resistance of the material drops to zero. At this temperature and below, the material is said to be a superconductor.

Explain the instantiate of a closed circuit

When a circuit is turned on, the voltage of the power source creates an electric field everywhere in the circuit. The field travels at or near the speed of light. Electrons everywhere in the circuit experience a force because of this field. Therefore, the electrons everywhere begin to move

What scientist is related to frog legs? to discovering the battery?

_ Luigi Galvani (touched two metals together and made frog leg twitch) - Alessandro Volta found that the frog legs had nothing to do with it, it was the two metals and discovered the battery

A changing magnetic field in free space (e.g., a vacuum) induces

a changing electric field

Explain field induction

a changing magnetic field produces an electric field' a changing electric field produces a magnetic field - produces an electromagnetic wave, which is always perpendicular to each other and travels until it hits something - produces electromagnetic radiation

Explain electromagnetic induction

a changing magnetic field through closed coil induces an electric current through the coil

What is an electric charge?

a fundamental property of subatomic particles

Moving electric charges are surrounded by

a magnetic/ electric field

If you change the magnetic field inside a closed loop of wire, you induce ___________ in the loop.

a voltage/ a current.

What is a galvanometer called with it is calibrated to read current? What about to read voltage?

ammeter, voltmeter

According to Ohm's law, if the resistance of a circuit increases, the current through the circuit

decreases

What is the only way an electric charge will experience a force by a magnetic field?

by being perpendicular to the field

WHat has more resistance: wet or dry skin?

dry

Define conductors and insulators. Give examples

conductors: - allow charges to move easily - metals and plasmas insulators: - don't allow charges to move easily - rubber

The unit of electric charge is the ________

coulomb

What is Ohm's Law?

current is directly proportional to voltage and inversely proportional to resistance

If you were to cut a bar magnet in half,

each piece would be a magnet with both north and south poles

Give two examples of common force fields.

electric and gravitational

Which "flows" through an electric circuit: voltage, electric charge, resistance, or all three?

electric charge

Which travels at nearly the speed of light in an electric circuit: electrons, the electric field, or both?

electric field

The electric current in a wire is normally composed of __________.

electrons

A likely cause for the existence of Earth's magnetic field is

moving charges in the liquid part of Earth's core

What produces a magnetic field?

moving electric charge

An iron nail is more strongly attracted to the

north or south pole - no difference really.

What are the charges of protons/electrons/neutrons?

p= positive n= neutral e= negative

A neutral glass rod is rubbed with silk. The silk removes electrons from the rod, thereby charging it. What kind of charge does the rod acquire through this interaction?

positive charge

Electric fields "begin" on __________ charges and "end" on ___________ charges.

positive; negative

Like electric charges ________ and opposite electric charges _________.

repel; attract

What is electric potential energy? What is its unit>

the energy associated with the position of the electric charge/ joule (J)

The resistance of a wire depends on

the length of the wire. the temperature of the wire. the radius of the wire.

What happens to the direction of the magnetic field around an electric current when the direction of the current is reversed?

the magnetic field direction reverses

Which has the greater resistance, a thick wire or a thin wire of the same length?

the thin wire has the greater resistance.

The amount of current in a circuit depends on ____________.

the voltage across the circuit. The resistance of the circuit.