[The note has been updated for syllabus].
All the questions in the past exam papers were analysed and there were a large amount of repetitive questions; the most noticeable ones being the definitions and the topic of ultrasound. For ultrasound this note consists of all the possible question and...
Is there anything I can do to improve the notes? I'll try my best to add them!
By: nanikmahajan • 5 year ago
By: pete_lohprasert • 5 year ago
Can you please tell me how the notes could be improve so that I can edit it during this summer holiday. Thanks!
By: mohammadsadat2001 • 5 year ago
By: eimanhamdoun • 5 year ago
By: pete_lohprasert • 5 year ago
I am sorry to see that you didn't like my notes, can you perhaps tell me what you think could be improved so that I can edit it over the summer holiday for the future students who take the exams. Thanks!
Show more reviews
Seller
Follow
pete_lohprasert
Reviews received
Content preview
Physics A2 Paper 4 Notes
Last Edited: 13/2/2019
Patapee Lohprasert (pete.lohh@gmail.com)
Mechanical Engineering Department, Imperial College London
,1 Gravitational Fields and Electric Fields
1.1 Important Definitions
Field of force: region (of space) where a force is experienced by a particle
Gravitational Field: region of space where a mass experiences a force
Gravitational Field Strength: Force per unit mass
Electric field strength: force per unit positive charge acting on a stationary charge
Gravitational potential: work done in bringing unit mass from infinity to the point
Electric potential: work done/ energy in moving unit positive charge from infinity to the
point
Newton’s law of gravitation: force proportional to product of the two point masses and
inversely proportional to the square of their separation
Coulomb’s Law: force proportional to product of charges and inversely proportional to
square of separation
𝑞1 𝑞2
1. 𝐹 = (Electrical Force 𝐹, 𝜖0 = 8.85 × 10−12 )
4𝜋𝜖0 𝑟 2
𝑉
2. 𝐸 = (Electric Field Intensity 𝐸, distance of two charged
𝑑
plates, 𝑑)
𝑄
3. 𝑉 = (Electric Potential 𝑉)
4𝜋𝜖0 𝑟
1.3 Exam Style Questions and Key Points
State what is meant by a line of force in
• A gravitational field: tangent to line gives direction of force on a small test mass
• An electric field: tangent to line gives direction of force on a small positive test
charge
Similarities and differences between gravitational force field and electric force field
around a charged metal sphere isolated in space.
• Similarities:
, • radial fields
• lines normal to surface
• greater separation of lines with increased distance from sphere
1
• field strength ∝
(𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑜 𝑐𝑒𝑛𝑡𝑟𝑒 𝑜𝑓 𝑠𝑝ℎ𝑒𝑟𝑒)²
• Differences:
• gravitational force (always) towards sphere
• electric force direction depends on sign of charge on sphere (towards or away
from sphere)
Why gravitational potential is a negative quantity:
• Gravitational potential at infinity is zero
• Gravitational force attractive so work done as object moves from infinity so potential
is negative
• OR, gravitational force is (always) attractive
• work is done is by masses so negative as they come together
Why the electric field strength in metal sphere is zero
• charges in metal do not move
𝐹
• no (resultant) force on charges so no (electric) field (as 𝐸 = )
𝑄
Why points outside an isolated spherical conductor, the charge on the sphere may be
considered to act as a point charge at its centre:
• lines perpendicular to surface OR, lines are radial
• lines appear to come from center
2 Magnetic Fields
2.1 Important Definitions
Tesla: uniform magnetic flux normal to long straight wire carrying a current of 1A creates
force per unit length of 1 Nm^-1
Faraday’s law: Induced e.m.f is directly proportional to the rate of change of magnetic flux
∆𝑁𝛷
linkage. (𝑉 = )
∆𝑡
Lenz’s law: induced e.m.f./current produces effects in a direction that opposes the change
causing it
Quantisation of charge: charge exists in discrete and equal quantities
1.2 Key Equations
1. 𝐹 = 𝐵𝐼𝐿 (Magnetic Force 𝐹, Magnetic Field Strength 𝐵, length 𝐿)
, 2. Ф = BA (Magnetic flux Ф, Area 𝐴 perpendicular to 𝐵)
3. Flux linkage = ФN (𝑁 = number of turns)
2.3 Exam Style Questions and Key Points
Magnetic field of Earth is always horizontal unless at the poles.
Why a Hall probe is made from a thin slice of material
• Hall voltage depends on thickness of slice
• thinner slice, larger Hall voltage
Why is it difficult to detect hall voltage in a thin slice of copper:
• (in metal,) n is very large
• (therefore) hall voltage is small
Value of the Hall Voltage:
• Hall voltage depends on angle between field and plane of probe
• Max when field normal to plane of probe
Explain why the r.m.s value of the current in the solenoid is reduced as a result of inserting
an iron core:
• For same current iron core gives larger rate of change of flux linkage (iron core
increase the magnetic field strength -> increases flux density)
• e.m.f induced in solenoid is greater (for same current)
• induced e.m.f. opposes applied e.m.f. so current smaller/acts to reduce current
As the magnet is being moved into the solenoid, thermal energy is transferred in the
resistor. Use laws of electromagnetic induction to explain this thermal energy:
• moving magnet gives rise to/causes/induces e.m.f./current in solenoid/coil
• (induced current) creates field/flux in solenoid that opposes (motion of) magnet
• work is done/energy is needed to move magnet (into solenoid)
• (induced) current gives heating effect (in resistor) which comes from the work done
Two wires are laid side-by-side and carry equal currents I in opposite directions, explain
why the total magnetic flux density due to the current in the wires is negligible:
• magnetic fields are equal in magnitude/strength/flux density
• magnetic fields are opposite in direction
• fields superpose/add/cancel to give zero/negligible resultant field
Why magnet falling down through Aluminum takes longer to fall than and plastic tube :
• as magnet falls, tube there is a change in magnetic flux
, • (different rate of change of magnetic flux at different part of tube so there is p.d and)
eddy current induced in aluminum tube but current can’t flow in plastic tube
• eddy current causes heating effect
• heat energy derived from KE of falling magnet
• terminal velocity decreases so longer time in aluminum
Reduction in amplitude of oscillation when a metal block cuts a magnetic field:
• metal block cut magnetic flux at different rate so different induced emf at different
part
• give rise to eddy current which causes heating effect
• heat energy derived from energy of oscillation
3 Circular Motion
3.1 Important Definitions
Radian: angle subtended from centre of a circle where arc length is equal to the radius
3.3 Exam Style Questions and Key Points
Path of the electron in the magnetic field is in the arc of a circle
• (magnetic) force (always) normal to velocity/direction of motion
• (magnitude of magnetic) force constant // speed is constant / kinetic energy is
constant
• magnetic force provides/is the centripetal force
• OR :
• Force due to magnetic field is constant
• Speed of particle is constant
• Force always normal to direction of motion
• Magnetic force provides centripetal force
Speed of particle in arc is not affected by magnetic field :
• Magnetic field always perpendicular to direction of motion
• so there is no work done on the particle
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller pete_lohprasert. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $14.99. You're not tied to anything after your purchase.
