Whiteboard Warmup!I II

In the scenarios shown above, two identical magnets are held near two identical loops of conducting wire. In case I, the magnet is held a distance x from the loop, and in case II, is held a distance 2x from the loop. Which of the following is true?

(A)In case I, the wire will have twice the induced current as in case II.(B)In case II, the wire will have twice the induced current as in case I.(C)In case I, the wire will have a greater induced current, but not twice as great.(D)In case II, the wire will have a greater induced current, but not twice as great.(E)Neither wire will have any current induced in it.

Whiteboard Warmup!

I II

(A) In case I, the wire will have twice the induced current as in case II.(B) In case II, the wire will have twice the induced current as in case I.(C) In case I, the wire will have a greater induced current, but not twice as great.(D) In case II, the wire will have a greater induced current, but not twice as great.(E) Neither wire will have any current induced in it.

Current is caused by a change in magnetic flux!

There is no change in flux in either case!

v v v

Motional EMF WhiteboardA rectangular loop of wire is made to move at a constant

velocity into, through, and out of the magnetic field shown below.

v v v

I: CW I: CCWI: Zero

No change in magnetic flux

v v v

I I

Round II!What will be the direction of the net magnetic force

exerted the cart at each of the points shown?

Hint: You will need to use RHR #2 for each segment of current-carrying wire that is in the B-field

v v v

FB FB

The net magnetic force will oppose the loop of wire entering the field, and then oppose the loop of wire leaving the field!

There is zero net magnetic force while the cart is completely within the B field.

You will have to push the cart into the field, then let it glide through the field, and finally you have to pull it out!

A square loop of wire of resistance R and side a is oriented with its plane perpendicular to a magnetic field B, as shown above. What must be the rate of change of the magnetic field in order to produce a current I in the loop? 

(A) IR/a2 (B) Ia2/R (C) Ia/R (D) Ra/I (E) IRa

A neutral loop of conducting wire is moved through a uniform magnetic field as shown below. What will happen as a result?

vB

(A) A clockwise current will flow around the loop

(B) A counterclockwise current will flow around the loop

(C) The top of the loop will become positively charged and the

bottom of the loop will become negatively charged.

(D) The top of the loop will become negatively charged and the

bottom of the loop will become positively charged.

(E) None of the above.

vB

Since it is a conductor, we know that the electrons are mobile.

Since the electrons are moving to the right in the B-field, we can use RHR # 2 to determine that…

The electrons within the conductor will feel an upward force!

vB

The electrons within the conductor will feel an upward force!

They will flow to the top of the conductor, giving it a net negative charge.

This will leave the bottom of the conductor with a net positive charge.

Test Tomorrow: Magnetism and EM Induction

1. Magnetic field of a current-carrying wire• RHR #1• B = (μ0I)/(2πr)• Superposition of fields

2. Magnetic force felt by a particle and wire• RHR #2• FB = qvBsinθ

• FB = BILsinθ• Force exerted between two wires

Test Tomorrow: Magnetism and EM Induction

4. Circular motion in a B-field• r = (mv)/(qB)• WB = 0 J

5. Crossed E and B fields• vundeflected = E/B• What happens if too slow, too fast.

3. Determining the direction of the B field, given the force, charge and velocity.

Test Tomorrow: Magnetism and EM Induction

7. Lenz’s Law• What causes an induced current?• RHR #3• Direction of Binduced, Iinduced

8. Faraday’s Law• |εinduced| = |ΔΦ/Δt|

6. Magnetic flux• Conceptually• Φ = BAcosθ

9. Motional emf• |εinduced| = Blv

This test will be a major grade, and the final grade of MP3.

There will be no grade improvements.

If you completed the last treasure hunt, 2 bonus points will be added onto your test grade.

If you completed the in-school treasure hunt,1 bonus point will be added onto your test grade.

Don’t forget to study RHR #2

Thumb: CurrentFingers: Field

Palm: Push

Also know how to use it with negative charges

moving in B-fields!

Spring Break Assignment:

Nuclear PhysicsSet aside at least five hours to complete the assignment!

There will be a test that includes nuclear physics when we return.

The material is very interesting, but it is brand new – you need to do all of the reading,

otherwise none of it will make sense.

There is a packet of multiple choice and free response questions that goes along with the reading.

The packet will be collected and graded on the day we return.