Grade 12 High School - General Physics 2 Notes

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GENERAL‌‌PHYSICS‌‌2‌ ‌ Charge‌‌Polarization‌ ‌
‌ One‌‌step‌‌(first)‌‌of‌‌charging‌‌by‌‌induction.‌ ‌
Lesson‌‌1:‌‌Electric‌‌Forces‌‌and‌‌Fields‌ ‌ ex.‌‌charged‌‌comb‌‌attracts‌‌an‌‌uncharged‌‌piece‌‌of‌‌paper‌‌(which‌‌is‌‌an‌
‌ insulator‌‌so‌‌no‌‌electrons‌‌will‌‌flow‌‌through‌‌it)‌ ‌
Electric‌‌Charge‌ ‌ ‌
Fundamental‌‌property‌‌of‌‌matter.‌ ‌ Coulomb’s‌‌Law‌ ‌
Describes‌‌the‌‌“electric-ness”‌‌of‌‌particles.‌ ‌ An‌‌electric‌‌charge‌‌exerts‌‌a‌‌force‌‌of‌‌attraction‌‌or‌‌repulsion‌‌on‌‌other‌‌electric‌‌
‌ charges.‌ ‌
Types‌‌of‌‌Charges‌ ‌ ‌
Kq q
Benjamin‌‌Franklin‌‌stated‌‌that‌‌there‌‌are‌‌two‌‌charges,‌‌positive‌‌and‌‌negative.‌ ‌ F = r12 2 ‌
Like‌‌charges‌‌repel,‌‌unlike‌‌charges‌‌attract.‌ ‌ ‌k‌‌=‌‌9.0‌‌x‌‌10‌9‌‌ ‌N‌‌m2‌‌ ‌ ‌/‌‌C2‌‌ ‌ ‌(Coulomb‌‌constant)‌ ‌
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Elementary‌‌Charge‌ ‌ Electric‌‌Field‌ ‌
e‌‌=‌‌1.60‌‌x‌‌10‌19‌Coulomb‌
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‌ Is‌‌a‌‌vector‌‌and‌‌is‌‌denoted‌‌by‌E‌ .‌ ‌
‌ If‌‌positive‌‌(proton),‌‌it‌‌is‌‌radially‌‌outward.‌ ‌
Particle‌‌Charges‌ ‌ If‌‌negative‌‌(electron),‌‌it‌‌is‌‌radially‌‌inward.‌ ‌
Proton‌ +‌‌e‌‌=‌‌+‌‌1.60‌‌x‌‌10‌19‌‌ ‌C‌ ‌ ‌
Electron‌ -‌‌e‌‌=‌‌-‌‌1.60‌‌x‌‌10‌19‌‌ ‌C‌ ‌
Neutron‌ no‌‌charge‌ ‌
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Properties‌‌of‌‌Electric‌‌Charge‌ ‌
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1.‌‌Charge‌‌comes‌‌in‌‌quantized‌‌units.‌ ‌
Charge‌‌comes‌‌in‌‌multiples‌‌of‌‌e‌‌(...,‌‌-2e,‌‌-1e,‌‌0e,‌‌+1e,‌‌+2e,‌‌…)‌ ‌
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Quarks‌ ‌
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Matter‌‌contains‌‌atoms.‌ ‌
(a)‌‌is‌‌a‌‌dipole;‌‌(c)‌‌is‌‌not,‌‌-e‌‌has‌‌less‌‌electric‌‌field‌‌lines‌‌than‌‌+e.‌ ‌
Atoms‌‌contain‌‌electrons‌‌and‌‌a‌‌nucleus.‌ ‌
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An‌‌atom’s‌‌nucleus‌‌contains‌‌protons‌‌and‌‌neutrons.‌ ‌
Electric‌‌Field‌‌Line‌ ‌
Protons‌‌and‌‌neutrons‌‌contain‌‌quarks.‌ ‌
Set‌‌of‌‌continuous‌‌lines‌‌that‌‌are‌‌always‌‌parallel‌‌to‌‌the‌‌electric‌‌field.‌ ‌
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They‌‌are‌‌not‌‌real.‌ ‌
Types‌‌of‌‌Quarks‌ ‌
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Top‌ (⅔)‌‌e‌ Bottom‌ (-⅓)‌‌e‌ ‌
Notes‌ ‌
Charm‌ (⅔)‌‌e‌ Strange‌ (-⅓)‌‌e‌ ‌
1. Must‌‌begin‌‌on‌‌a‌‌“positive”‌‌charge‌‌and‌‌end‌‌on‌‌a‌‌“negative”‌‌charge.‌ ‌
Up‌ (⅔)‌‌e‌ Down‌ (-⅓)‌‌e‌ ‌
2. Magnitude‌‌of‌‌an‌‌electric‌‌field‌‌is‌‌the‌‌largest‌‌for‌‌the‌‌field‌‌of‌‌lines‌‌
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that‌‌are‌‌most‌‌closely‌‌spaced‌‌near‌‌the‌‌charges.‌ ‌
Protons‌‌contain‌‌2U‌‌and‌‌1D.‌ ‌
3. Never‌‌intersect‌‌each‌‌other.‌ ‌
Neutrons‌‌contain‌‌1U‌‌and‌‌2D.‌ ‌
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The‌‌presence‌‌of‌‌a‌‌charge‌‌produces‌‌an‌‌electric‌‌field.‌ ‌
2.‌‌Charge‌‌is‌‌conserved.‌ ‌
Electric‌‌field‌‌is‌‌related‌‌to‌‌the‌‌electric‌‌force.‌ ‌
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Law‌‌of‌‌Conservation‌ ‌
Charge‌‌can‌‌move‌‌from‌‌place‌‌to‌‌place,‌‌and‌‌from‌‌one‌‌object‌‌to‌‌another,‌‌ F = ∣q ∣ E → E = ∣Fq∣ ‌
K ∣Q∣
but‌‌the‌‌total‌‌charge‌‌of‌‌the‌‌universe‌‌does‌‌not‌‌change.‌ ‌ ‌E = r2 Units:‌‌Newton‌‌per‌‌Coulomb‌‌(N/C)‌ ‌
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Electrons‌‌are‌‌the‌‌one‌‌being‌‌transferred,‌‌not‌‌protons,‌‌because‌‌they‌‌are‌‌ ‌
not‌‌attached‌‌in‌‌the‌‌atom’s‌‌nucleus.‌ ‌ ‌
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Types‌‌of‌‌Charging‌ ‌
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1.‌‌Charging‌‌by‌‌Contact‌ ‌
Transfer‌‌of‌‌a‌‌charge‌‌from‌‌one‌‌material‌‌to‌‌another‌‌by‌‌physical‌‌contact‌‌
between‌‌materials.‌ ‌
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How‌‌to‌‌make‌‌an‌‌object‌‌positively-charged?‌‌Move‌‌a‌‌positively-charged‌‌
object‌‌such‌‌as‌‌glass‌‌(which‌‌is‌‌usually‌‌positive,‌‌while‌‌rubber‌‌or‌‌plastic‌‌is‌‌
usually‌‌negative).‌‌The‌‌negative‌‌charges‌‌from‌‌the‌‌object‌‌will‌‌be‌‌
transferred‌‌to‌‌the‌‌glass.‌ ‌
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2.‌‌Charging‌‌by‌‌Induction‌ ‌
Process‌‌of‌‌giving‌‌one‌‌object‌‌a‌‌net‌‌electric‌‌charge‌‌without‌‌touching‌‌the‌‌
object‌‌to‌‌a‌‌second‌‌charged‌‌object.‌ ‌
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For‌‌example,‌‌this‌‌is‌‌done‌‌when‌‌a‌‌negatively-charged‌‌object‌‌is‌‌moved‌‌
near‌‌another‌‌object,‌‌polarizing‌‌it.‌‌The‌‌electrons‌‌move‌‌away‌‌into‌‌a‌‌
grounding‌‌path‌‌or‌‌wire,‌‌which‌‌makes‌‌the‌‌object‌‌positively-charged.‌ ‌
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Lesson‌‌2:‌‌Electric‌‌Potential‌ ‌ Equipotential‌‌Lines‌‌and‌‌Surfaces‌ ‌
‌ An‌‌equipotential‌‌surface‌‌is‌‌a‌‌3D‌‌surface‌‌on‌‌which‌‌the‌‌electric‌‌potential‌‌V‌‌is‌‌
Battery‌ ‌ the‌‌same‌‌at‌‌every‌‌point.‌ ‌
The‌‌positive‌‌side‌‌is‌‌called‌‌positive‌‌potential,‌‌negative‌‌side‌‌is‌‌negative‌‌ Electric‌‌field‌‌lines‌‌and‌‌equipotential‌‌surfaces‌‌are‌‌always‌‌perpendicular.‌ ‌
potential.‌ ‌ ‌
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Electric‌‌Potential‌‌Energy‌ ‌ BOOK‌ ‌
When‌‌a‌‌charged‌‌particle‌‌moves‌‌in‌‌an‌‌electric‌‌field,‌‌the‌‌field‌‌exerts‌‌a‌‌force‌‌ ‌
that‌‌can‌‌do‌‌work‌‌on‌‌the‌‌particle.‌‌The‌‌work‌‌is‌‌the‌‌PE‌elec‌ ‌ Capacitance‌ ‌
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Since‌‌electric‌‌force‌‌is‌‌conservative,‌‌similar‌‌to‌‌the‌‌gravitational‌‌force,‌‌then‌ ‌
ΔP E elec = − W = − F elec Δx ‌
ΔP E elec = − q EΔx ‌
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If‌‌two‌‌charges‌‌are‌‌initially‌‌separated‌‌by‌‌a‌‌distance‌r‌ 1‌‌ ,‌‌then‌‌brought‌‌
together‌‌to‌‌a‌‌final‌‌separation‌r‌ 2‌‌ ,‌‌then‌ ‌
kq q kq q
ΔP E elec = P E elec2 − P E elec1 = r12 2 − r11 2 ‌
But‌‌is‌r‌ 1‌‌ ‌ ‌is‌‌in‌‌infinite‌‌(q‌1‌‌ ‌and‌‌q2‌‌ ‌ ‌are‌‌infinitely‌‌apart),‌‌then‌ ‌
kq q
P E elec = r1 2 ‌
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If‌‌we‌‌have‌‌a‌‌collection‌‌of‌‌point‌‌charges,‌‌the‌‌total‌‌PE‌elec‌‌ ‌is‌‌the‌‌sum‌‌of‌‌the‌‌
potential‌‌energies‌‌of‌‌each‌‌pair‌‌of‌‌charges.‌ ‌
kq q kq q
ΔP E elec = P E elec2 − P E elec1 = r01 1 − r02 2 ‌
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Electric‌‌Potential‌ ‌
Scalar.‌ ‌
Often‌‌referred‌‌to‌‌as‌‌simply‌‌the‌‌“potential”.‌ ‌
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ΔP E kqQ kQ 1 Q
V = q elec = 1q r = r = 4πε r
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0
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Unit:‌ Volt‌‌(V)‌ ‌
V‌‌=‌‌J/C‌‌or‌‌N‌‌m/C‌ ‌
1eV‌‌=‌‌1.60‌‌x‌‌10‌-19‌‌ ‌J‌ ‌
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ε‌0‌ ‌
Permittivity‌‌of‌‌free‌‌space,‌‌a‌‌constant.‌ ‌
How‌‌an‌‌electric‌‌field‌‌propagates‌‌or‌‌moves‌‌in‌‌empty‌‌space‌‌or‌‌a‌‌vacuum.‌ ‌
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Electric‌‌Potential‌‌‌and‌E‌ lectric‌‌Field‌ ‌
Magnitude‌‌and‌‌direction‌‌of‌‌electric‌‌field‌‌are‌‌related‌‌to‌‌how‌‌the‌‌electric‌‌
potential‌‌changes‌‌with‌‌position.‌ ‌
E‌‌is‌‌proportional‌‌to‌‌the‌‌rate‌‌of‌‌change‌‌of‌‌V‌‌with‌‌position.‌ ‌
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Potential‌‌Difference‌‌‌or‌V ‌ oltage‌ ‌
Scalar.‌ ‌
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ΔP E elec = − W = − q EΔx ‌
ΔP E
ΔV = q elec = − E Δx ‌
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Negative‌‌sign‌‌(-)‌‌indicates‌‌that‌‌the‌‌electric‌‌field‌‌goes‌‌from‌‌a‌‌region‌‌of‌‌
high‌‌potential‌‌to‌‌a‌‌region‌‌of‌‌low‌‌potential.‌ ‌
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Due‌‌to‌‌a‌‌Point‌‌Charge‌ ‌
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kq
V = r ‌
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Due‌‌to‌‌a‌‌Collection‌‌of‌‌Charges‌ ‌
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V =V1+V2+V3 ‌
kq kq kq
V = r11 + r22 + r33 ‌
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Due‌‌to‌‌Charged‌‌Conducting‌‌Sphere‌ ‌
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kq
Outside‌ V = r ‌
kq
Inside‌ V = R
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