What can electricity tell us? Magnetism What can electricity tell us?

Similarities to Electricity No touching force N/S is analogous to +/- Create field lines to help us keep track

Important Differences N/S cannot be separated! Measured in Teslas (special unit) not N/C (a derived unit) More than just magnetic poles experience a force

Just who does experience a force? Electricity: Charged particles Magnetism: Magnetic poles Moving charged particles There is an obvious connection between electricity and magnetism that shows up here!

Magnetic Field Lines Electricity: Force points in direction of field, always tangent to the field line Closer lines = stronger field Leave positive and land on negative Magnetism: Force points in direction of field, always tangent to the field line Closer lines = stronger field (called flux) Leave North and land on South

The Connection Continues… Who creates magnetic fields? Magnetic Poles Moving Charged Particles Electricity!

What do magnetic field lines look like? Magnetic Dipole: Near Current Carrying Wires:

Mapping other field lines… Perform the procedure to create your own magnetic field lines around two sets of magnets. Does the magnetic force follow an inverse square law?

The Direction of the Magnetic Field The Force, Field and Motion are ALWAYS orthogonal! Motion can be a moving individual particle or a current carrying wire Leads us to two equations:

Current Carrying Wire F = I l B sin θ F = Force I = current l = length of wire in the field B = Magnetic Field (Teslas) Θ = the angle between the field and current

Moving Charged Particle F = q v B sin θ F = Force q = charge v = velocity of particle B = Magnetic Field (Teslas) Θ = the angle between the field and velocity

The Right Hand Rule Since thumb, palm and fingers are orthogonal, they serve as a mnemonic device.

Field Lines Around a Wire Grab the wire with your thumb point in the direction of the conventional current. Fingers point in the direction of the magnetic field.

Forces on Wires and Particles Point Fingers in direction of the current or velocity. Point Palm in the direction of the magnetic field. Thumb points in the direction of the force.

Review Moving charged particles create magnetic fields. Moving charged particles in a magnetic field experience a force. Charged particles in an electric field experience a force. There must be some connection between them!

Michael Faraday Faraday did many experiments that lead to the connections between electricity and magnetism. Many of them were about electromagnetic induction.

Electromagnetic Induction If electricity (moving charged particles) creates magnetic fields, then maybe the opposite can be found to be true? Moving magnetic fields can create electricity; called electromagnetic induction.

Flux = magnetic field times the perpendicular area. Magnetic Flux Flux is defined as the number of magnetic field lines that perpendicularly intersect an area in space. FB = B A cos Q Flux = magnetic field times the perpendicular area.

Faraday’s Law A changing magnetic flux causes electricity. E = -N (D FB/ Dt) The induced emf (voltage) is related to the number of loops of wire times the rate in change of the magnetic flux.

How does the flux change? Since FB = B A cos Q, then: E = -N (D (B A cos Q) / Dt) So one of three things must be changing to induce a voltage: Magnetic Field (B) Area (A) Angle (Q)

Change the Magnetic Field Move in and out of a uniform magnetic field Move away or toward a magnetic pole Increase or decrease a current through a wire

Changing the Area Increase the size of the hoop Decrease the size of the hoop

Changing the Angle Rotate the hoop near a uniform magnetic field Rotate a hoop near a magnetic dipole

Magnetic Fields Due to Loops of Wire Already learned that current carrying wires create magnetic fields. Loops of wire with current create magnetic fields. The fields intersect the area of the loop and create flux. Use the right hand rule to determine the direction of the flux.

Faraday’s Law Revisited E = -N (D (B A cos Q) / Dt) This voltage induces a current in the wire: this is Faraday’s Law But what direction will the current move?

Lenz’s Law The direction of an induced current is such that the magnetic flux created by the current compensates for the flux change that created the current. It is the negative sign in Faraday’s Law E = -N (D (B A cos Q) / Dt)