Physics Mod 4 Electricity & Magnetism

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Electricity & Magnetism

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32 Terms

1
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Rules for field lines

1/ They point in the direction of the electric field

2/ They never cross

3/ Always flows from positive charges to negative charges

4/ The field strength is proportional to the density of field lines (arrows)

<p>1/ They point in the direction of the electric field</p><p>2/ They never cross</p><p>3/ Always flows from positive charges to negative charges</p><p>4/ The field strength is proportional to the density of field lines (arrows)</p>
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Electric Field Strength formula

E = F/Q

where

  • E: electric field strength (N/C)

  • F: (N)

  • Q: is the magnitude of the charge (coulomb)

<p><strong>E = F/Q</strong></p><p>where</p><ul><li><p>E: electric field strength (N/C)</p></li><li><p>F: (N)</p></li><li><p>Q: is the magnitude of the charge (coulomb)</p></li></ul><p></p>
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Uniform Electric Fields

E = V/d

where

  • E: Electric field strength (V/m)

  • V: Potential difference (V)

  • d: distance (m)

<p><strong>E = V/d</strong></p><p>where</p><ul><li><p>E: Electric field strength (V/m)</p></li><li><p>V: Potential difference (V)</p></li><li><p>d: distance (m)</p></li></ul><p></p>
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Coulomb’s Law

States that the electrostatic force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them

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Electric Current

A flow of electric charge in an electronic circuit, measured in Amps (A)

Basically, it is the rate at which charges are flowing per second.

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Equation for Current

I = Q / t

where

  • I is current (Amps)

  • q is charge (Coulumbs or C)

  • t is time (s)

<p><strong>I = Q / t</strong></p><p>where</p><ul><li><p>I is current (Amps)</p></li><li><p>q is charge (Coulumbs or C)</p></li><li><p>t is time (s)</p></li></ul><p></p>
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Voltage (Potential Difference)

A measure of electrical energy per charge in a circuit

Measured in Volts (V)

Basicallt how much energy each charged particle has

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Resistance

A measure of how difficult it is for electricity to pass through a material, measured in ohms

Resistance reduces Current NOT Voltage!!

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Ohm’s Law

  • R = V/I

  • V = IR

  • I = V/R

<ul><li><p>R = V/I </p></li><li><p>V = IR</p></li><li><p>I = V/R</p></li></ul><p></p>
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Power formulas

  • Power = Voltage x Current (P=VI)

  • Power = Energy/time (P=E/t)

  • V = V²/R

  • P = I²R

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Kirchhoff’s 1st Law

States that the sum of the current entering a point in a circuit is equal to the sum of the currents leaving a circuit.

  • ΣI_in = ΣI_out

Σ: Sum

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Kirchoff’s 2nd Law

otal Voltage in battery = Total Voltage in Resistors

  • ΣV_in Battery = ΣV_in Resistors

Σ: Sum

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The Law of Conservation of Energy

States that energy can neither be created nor destroyed, only transformed from one form to another.

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Resistance in series circuit

R(total) = R1 + R2 + R3 + …

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Resistance in Parallel circuit

1/R(total) = 1/R1 + 1/R2 + 1/R3 + …

<p>1/R(total) = 1/R1 + 1/R2 + 1/R3 + …</p>
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In a series circuit, Voltage is… Current is…

Current: constant

Voltage: splits

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In a parallel circuit, Voltage is… Current is…

Current: splits

Voltage: constant

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Magnetic poles - Where is the magnetic field the strongest?

Towards the ends of the magnet, poles are where the field is strongest (N & S)

  • That is why when placing two magnets together by its sides, they don’t attract/repel, whereas when you place the heads to tails, there is reaction force!

<p>Towards the <strong>ends of the magnet</strong>, <strong>poles are where the field is strongest (N &amp; S)</strong></p><ul><li><p>That is why when placing two magnets together by its sides, they don’t attract/repel, whereas when you place the heads to tails, there is reaction force!</p></li></ul><p></p>
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Magnetic Dipoles

When breaking a magnet in half, the two poles are separated, thereby producing a new pair of poles in the process.

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Law of magnetism

2 like poles always repel

2 unlike poles always attract

<p>2 like poles always repel</p><p>2 unlike poles always attract</p>
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Drawing Magnetic Fields (3 rules)

  1. The line starts at the North pole and end at South pole

  2. They never cross

  3. The spacing of the lines show the strength of the field (closer=stronger)

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Magnetic field around a wire (right hand grip)

This rule determines the direction of the magnetic field around a current-carrying wire: point your right thumb in the direction of the conventional current, and your curled fingers will show the circular path of the magnetic field lines

<p>This rule determines the direction of the magnetic field around a current-carrying wire: <strong><mark data-color="rgba(0, 0, 0, 0)" style="background-color: rgba(0, 0, 0, 0); color: inherit;">point your right thumb in the direction of the conventional current, and your curled fingers will show the circular path of the magnetic field lines</mark></strong></p>
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Magnetic Field for a Straight Current Carrying wire formula

B = μ₀I / (2πr)

B magnetic field

μ₀ is the permeability of free space (4π × 10⁻⁷ T·m/A)

I is the Current

r is the distance from the wire

<p><strong>B = μ₀I / (2πr)</strong></p><p></p><p>B magnetic field</p><p>μ₀ is the permeability of free space (4π × 10⁻⁷ T·m/A)</p><p>I is the Current</p><p>r is the distance from the wire</p>
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Solenoid

a long coil of many turns of a wire

<p>a long coil of many turns of a wire</p>
25
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Magnetic domains

  • A small region within a ferromagnetic material where the magnetic moments of its atoms are aligned in the same direction, creating an area of strong magnetisation.

(Remember the multiple compass experiment)

<ul><li><p>A<strong><mark data-color="rgba(0, 0, 0, 0)" style="background-color: rgba(0, 0, 0, 0); color: inherit;"> small region within a ferromagnetic material where the magnetic moments of its atoms are aligned in the same direction, creating an area of strong magnetisation</mark></strong>.</p></li></ul><p>(Remember the multiple compass experiment)</p><p></p>
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Methods by which ferromagnetic materials become magnetised

  1. Iron bar method

  2. Double touch method

  3. Electromagnetic method

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Ferromagnetic

Materials that can be strongly magnetised and are attracted to magnets, often forming permanent magnets

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Ferromagnetic materials

ie. iron, nickel, and cobalt are substances that are strongly attracted to magnets and can be permanently magnetised. This strong magnetism is due to aligned magnetic domains.

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Double touch method

One of the 3 methods to make ferromagnetic materials become magnetised.

Procedure: Two bar magnets with opposite poles facing each other are moved towards the ends of the steel bar, lift the magnets when they reach the ends of the steel bar, —> repeat 30 times.

<p>One of the 3 methods to make ferromagnetic materials become magnetised.</p><p><strong>Procedure</strong>: Two bar magnets with opposite poles facing each other are moved towards the ends of the steel bar, lift the magnets when they reach the ends of the steel bar, —&gt; repeat 30 times.</p>
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Electromagnetic method

One of the 3 methods to make ferromagnetic materials become magnetised.

Procedure: Wrap a wire around an iron nail and running current through the wire, don’t overlap the wire and make sure tightly wrapped

(remember the paperclip experiment on dump post)

<p>One of the 3 methods to make ferromagnetic materials become magnetised.</p><p><strong>Procedure</strong>: Wrap a wire around an iron nail and running current through the wire, don’t overlap the wire and make sure tightly wrapped</p><p>(remember the paperclip experiment on dump post)</p>
31
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Electrical Current vs Conventional Current

Conventional current: Positive charges flow from positive to negative terminal

Electron current: Negative charges flow from negative to positive terminal

<p><strong>Conventional current</strong>: Positive charges flow from positive to negative terminal</p><p><strong>Electron current:</strong> Negative charges flow from negative to positive terminal</p>
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Iron bar method

One of the 3 methods to make ferromagnetic materials become magnetised.

Procedure: An iron bar is rubbed with a magnet repeatedly in one direction.

<p>One of the 3 methods to make ferromagnetic materials become magnetised.</p><p><strong>Procedure: </strong>An iron bar is rubbed with a magnet repeatedly in <strong><u>one direction</u></strong>.</p>