一个ll AP Physics C Electricity Resources
Example Questions
Example Question #1 :Calculating Magnetic Fields And Forces
一个n infinitely long wire has a current ofrunning through it. Calculate the magnetic field at a distanceaway from the wire.
For infinitely long wires, the formula for the magnetic field is, whereis the current and线的距离。
The magnetic field is calculated using our given values.
Example Question #1 :Calculating Magnetic Fields And Forces
一个solenoid islong and it is made up ofturns of wire. How much current must run through the solenoid to generate a magnetic field ofinside of the solenoid?
The formula for the magnetic field inside the solenoid is, whereis the number of turns of wire,is the length of the solenoid, andis the current.
We want to find the current so we solve for.
Plug in the values.
Example Question #1 :Calculating Magnetic Fields And Forces
Two parallel wires a distanceapart each carry a current, and repel each other with a forceper unit length. If the current in each wire is doubled to, and the distance between them is halved to, by what factor does the force per unit length change?
Relevant equations:
Step 1: Find the original and new magnetic fields created by wire 1 at wire 2, using Ampere's law with an Amperian loop of radiusor, respectively.
Original
New
Since the wires are parallel to each other and wire 1's field is directed circularly around it, in each case wire 1's field is perpendicular to wire 2.
Step 2: Find the original and new magnetic forces per unit length on wire 2, due to the field created by wire 1.
Original
New
So, the new force per unit length is 8 times greater than the original.
Example Question #11 :Magnetism
一个region of uniform magnetic field,, is represented by the grey area of the box in the diagram. The magnetic field is oriented into the page.
一个stream of protons moving at velocityis directed into the region of the magnetic field, as shown. Identify the correct path of the stream of protons after they enter the region of magnetic field.
一个semi-circular path oriented horizontally into the page
一个semi-circular path oriented vertically upward
一个semi-circular path oriented vertically downward
一个semi-circular path oriented horizontally out of the page
一个semi-circular path oriented vertically upward
The magnetic force on a moving charged particle is given by the equation:
Isolating the directional component of this equation yields the understanding that the resulting force on a moving charged particle is perpendicular to the plane of the velocity vector and magnetic field vector. Using the right-hand-rule on this cross-product shows that the velocity vector right-crossed into the magnetic field vector into the page yields a magnetic force vector upward on a positive charge. This will result in a semi-circular path oriented vertically upward.
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