 Magnetism 08 - Ampere's Law REVIEW & Solenoids

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M/c O' the Day:

Today's Safari Guide is:

JUSTIN!

2016 Released Exam Problem #8 ════════════════════

OPENING QUESTION: Please make a side by side list of attributes that apply when we're using the BS Law and attriutes that must be present in order to use Ampere's Law:

 BS vs A Law Analysis

Notice that this image does NOT show how to "cross" one quantity into another.

Having said that, what DOES this image illustrate? Let's review THIS: Please turn to the person next to you and suggest an explanation:

1) that shows how B and ds are actually in the same direction

2) why we *dot* B and ds

Now please consider THIS problem: A thin, straight wire of finite length carries a constant current I=2.15 A. Determine the magnitude & direction of the magnetic field at some point P => .25 meters away from the wire as shown above.

Setting up this problem should be pretty straightforward... why is that?

ANSWER: OBJECTIVES:

I will be able to explain Ampere's Law and do basic problems related to it during today's class.

I will be able to explain the basic workings of a solenoid during today's class.

I will be able to make basic "B"-field calculations involving solenoids during today's class.

WORDS/FORMULAE FOR TODAY

TERMS

• Magnetic Field (B): A vector value
• Magnetic Force (FB): Also a vector

CONSTANTS:

UNITS:

• Tesla = T defined as 1 N/C(m/s)

FORMULAE:

• B ds = μoI: Ampere's Law
• FB = qv x B
• FB = qvB
• FB = qvBsinθ
• FB = IL x B
• FB = ∫I ds x B NOTE: AP Version is: FB = ∫I d x B
• v = E/B
• τ = IAB (torque in a current carrying loop)
• τ = NIA x B (torque in a current carrying loop - vector version)
• τ = μ x B (torque in a current carrying loop - abbreviated version)
• KE = q2B2R2/2m
• dB = (μoI/4π)(d x r̂ )/r2 (BS Law)
• B∮ds = μoI
• B = μo(N/ℓ)I=μonI

WORK O' THE DAY

Solenoid as a circuit breaker is HERE

Do a wee bit of work on your chromies to see how a solenoid is essential for starting your car...

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HOMEWORK:

Begining on page 926:

1. explain why you have to use BS and and AL to do 30.11
2. do problem 30.33
3. do problem 30.41
4. do problem 30.39 (This one is a bit out of order... I got *very* close but I gotta an "oopsie" somewhere... see if you can do better!)
5. Check the AP C equation sheets and see IF and HOW solenoid type thingy equations are mentioned or will you have to derive and/or understand them instead

ANSWERS:   STUDY GUIDE: