Electromagnetic induction

Here is the link to a video on how soft iron core helps to increase the induced emf in the secondary coil

Change in flux

The word change means you have to know before and after.
Case1
If I turn the coil 30 degrees. The change in flux is flux after - flux before. It is never the flux at the 30 degree position.
Since flux is BA (before) and BAcos30 (after) the change is (1-0.866)BA which is 0.134 BA. Rate of change of flux is dividing the change by time taken. If the time taken is 0.1s , the induced e.m.f = 1.34 NBA= 1.34(50 x 0.18T x 0.02)= 0.24 V
Case2
A 180 degrees turn would mean a change of + BA to -BA which amount to 2BA. (Similar to the change of momentum of 2 mv when the ball bounces back). The induced e.m.f = 2NBA/0.1s = 3.6 V

These values are average induced e.m.f.
Case 3(with ref. to case 2)
The maximum induced e.m.f of coil = BANw where w the angular velocity can be calculated as 180(pi rad) /0.1s = 31.4 rad per s.The maximum induced emf = 5.65 V
pic taken from http://www.rfcafe.com/references/electrical/Electricity

Force on electron on wing tip

The aeroplane is heading NOrth. The Earth horizontal component is vertically down. Consider an electron in the wingspan acting like a rod. Using Fleming's LHR , the force on the electron is to the left side. The electron forced to the East wing tip will make it a negative potential , giving you the same result as using induced e.m.f method.
Note: The electron in the wingspan moving moving North require the current to point south(into the pic) when using LHR.

Induced e.m.f at wing tips

The aeroplane is heading North. Consider the wingspan like a rod, and Earth magnetic field to be vertically down . The horizontal component is along the direction of motion and therefore does not induced e.m.f. Using your Fleming's RHR , the induced current flow to the West wing(on your right side) , the West wing is the positive wing and East wing negative potential. The orientation is NSEW and therefore do not use right or left side.

Hall effect

The magnetic force causes the charge carrier to build up at 2 surfaces giving rise to Hall voltage. Depending on the polarity of the Hall voltage the type of charge carrier present in the wafer can be determined.
An equilibrium is acheived when the magnetic force is equal to the electric force . The electric force is due to the electric field arising from the Hall voltage.

Rotating coil

A coil rotating in a magnetic field must produce change in flux resulting in induced emf . Imagine the plane of the coil as the palm of your hand. Does the rotation of your palm change the area perpendicular to the B field. If it doesn't then no induced emf.

Electromagnetic induction

When a coil is rotated in such a way that there is a change in Area perpendicular to the magnetic field , there will be change in magnetic flux that will produced induced emf. The equation in general is E = NBAw sinwt. The maximum induced emf Eo= NBAw. Since this is sinuisoidal the rms voltage can be found .
The position of the coil when the emf is a max is when the flux is zero. At this location the plane of coil is parallel to B.

Fleming's Left hand or right hand rule

Induced current produced will oppose the change producing it ... Lenz'z law. The direction of induced current can be found using Fleming's right hand rule . It can also be found if Lenz's law states that the opposing force is produced by this current. In that case to find the direction of current can be found using the known direction of the opposing force using Fleming's left hand rule.

Earth field

The Earth's magnetic field acts as a shield from charged particles from outer space. Charged particles move along magnetic field lines. These lines do not enter Earth except at the poles.

Aurora borealis

<
Electrons ionise the atmosphere as they travel along magnetic field lines of the Earth. The sky lights up as a result of ionisation of the atmosphere. This effect is visible at the poles where the magnetic field lines are vertical .
Picture of the day.

Lenz's law

Try out this interesting applet!

B vector

Interesting applets to try out!

Metal dectectors

Metal detectors works on the concept in EMI . Induced current in metal produces magnetic field that would interfere with the existing magnetic field. This change can be detected and the user can be alerted .
Try out this applet!

Magnetic braking

How it feels like to use magnetic braking system? Have you tried some machines with magnetic braking system. Got to try it to know how it feels different from normal braking system.

EMI

taken from Wiki pic
The general formula is used for type of conductor but for a straight conductor you can use E= Blv. The direction of induced e.m.f can be determined using right hand rule or using Lenz law. From Lenz's law , you can deduce the induced current because of the fact that the induced current flow in Bfield to oppose the change producing it. If you hold out you left and right hand rule in front of you. Align the index finger (Bfield) and Middle finger (current)on both hand , you will find the thumb from both hands opposing each other . This shows that the force produced by current opposes the motion producing it. This satisfy conservation of energy as mechanical energy is required to oppose magnetic force in order to generated induced current.

Hand rules

To simplify , only mention 2 hand rules , dynamo (right hand) and motor (left hand) . The other rules can be ignored.
If you need to find direction of B produced by a current, use the your right hand to help you. The thumb can represent the I and fingers B for straight conductor. The thumb can represent B and the fingers I for a solenoid. Using your right hand for this purpose comes naturally when you wnat to find the source of B due to current. Avoid giving names like right hand grip rule or Maxwell screw rule to simplify matters.

Induced e.m.f

The Right Hand rule is applied to find the induced current produced by the induced e.m.f . To know the induced e.m.f polarity , we need to know how current flow inside the 'battery'. The current flow from negative to positive inside the battery(the moving bar) . Further confirm by considering how current would flow outside the battery (the fixed bar), it flows out from the positive terminal to the negative terminal. With these two ways of confirming the polarity , you cannot be wrong.
The top end is positive and the bottom end is negative on the moving bar.

Rate of change of flux linkage

Flux Linkage NBA. The rate of change of flux linkage can be compared to acceleration which is rate of change in velocity. The word rate refers to the time factor. The word change refers to the difference between the initial and final flux . These two factors change and rate are to be considered carefully. The gradient of the graph gives the magnitude and direction of the induced e.m.f.

Uniform field

The third time you hear uniform field. First in g field (around the surface) the field is considered uniform. Secondly in E field ( inside a pair of parallel plates charged with equal positive and negative charges on each side.Lastly in B field ( inside a solenoid) with coils carrying equal currents The formula may be given but mostly not necessary.

Magnetic field strength - B vector

Very often mistaken for magnetic field pattern. A straight conductor has circular magnetic field pattern, where its direction can be determined using the right hand thumb representing current direction and fingers showing the direction of field, clockwise or anticlockwise, The B vector a point near the conductor can be found by drawing the radial line and tangential to it is the B vector pointing to the direction of fingers.