Electricity & Magnetism 1 Flashcards
Conductor
Material that permits flow of charge
Charging by induction
Negatively charged rod brought near uncharged metal ball
Causes one side of ball + (closest to rod) and other -
If connect RHS with conducting wire to ground, charge will flow from ball to Earth
Disconnecting leaves + ball
Coulomb’s law
F=k|q1q2|/r^2
k=1/4piE0 = 9x10^9
Electric field
Force F0 that charge q0 feels at point, divided by charge
E=F0/q0
+ q0
Same direction for force and E0
-q0
Opposite directions for F0 and E0
Radial vector in electric field equation
E=k q/r^2 r^
r^ is like i^j^k^
Magnitude of radial vector
|r^|=1
Resultant field
Add components
Field lines
Away +
Towards -
Work done
W a—>b =Fd= q0Ed
Potential energy
U=k qq0/r
Or = k sum of qiqj/rij
Electric potential
V=U/q0
Potential= potential energy/charge
Inside sphere
No electric field
Graph of E against r for sphere
Start along x axis for inside sphere
Sloping down y axis after
Potential inside sphere
Same at every point inside
Graph of v against r
Constant whilst inside Spencer’s then slope down y axis once outside
Equipotential surface
Potential same at every point
Equipotential lines
Perpendicular to field lines (meet at right angles)
Stronger E field = closer together Equipotential
Potential gradient
E=- pot grad
If E is radial
Er=dv/dr
Need to calculate x,y and a components of E field
Moving charge produces
Magnetic field
Second moving charge
Experiences magnetic force
Unit of magnetic fields B
Tesla
Particle at rest
No magnetic field
Relation between F, B and v
F perpendicular to B and v (rh rule)
Cross product for F
qVxB
VxB found using 3x3 matrix discriminant
If both E and B
F=q(E+VxB)
Magnetic field lines
Parallel, straight, evenly spaced= uniform magnetic field
Into page
x
Out of page
o
Unit of magnetic flux
Webber (Wb)
Torque
t=IBAsin theta
Magnetic flux
I=BAcos theta
Ampere’s law
Integral B.dl = u0l enclosed
Comparing charged particles in mag filed with circular motion
F=|q|vB=mv^2/r
Pitch
Distance travelled along x axis in 1 rotation
=2pi/w
Magnetic moment
u=IA (A=area)
Anything that experiences a magnetic torque is often known as a magnetic dipole
Maximum torque that can be obtained with same total length of wire carrying same current in same mag field
Max will occur when A is max
Max area when area is a circle
Calculate circumference then radius and then plug in to equation for torque
