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Electricity and Magnetism

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Presentation on theme: "Electricity and Magnetism"— Presentation transcript:

1 Electricity and Magnetism
Physics 208 Dr. Tatiana Erukhimova Lectures 24, 25

2 Test 2 results Number of Students >90 >80 >70 >60 >50
>40 Score Average Median 68 Highest 99 Lowest 8

3 Electron motion in a microwave oven
A magnetron in a microwave oven emits electromagnetic waves with frequency f=2450 MHz. What magnetic field strength is required for electrons to move in circular paths with this frequency?

4 Using Crossed and Fields
Velocity selector independent of the mass of the particle!

5 Mass spectrometer

6 Thomson’s e/m experiment
1897: Cavendish Laboratory in Cambridge, England

7 Exercise 1 An electron, q=1.6 10-19C moves with velocity
It enters a magnetic field with What is the force on the electron?

8 Problem 5 Hall effect: The magnetic force on the charge carries in a wire can be used to determine their sign. Show that there will be an electric field, set up inside a wire in a magnetic field, that is perpendicular to the direction of the current. You should be able to show that the sign of the field depends on whether the mobile charges are positive or negative.

9

10 You place a slab of copper, 2. 0 mm thick and 1
You place a slab of copper, 2.0 mm thick and 1.5 cm wide, in a uniform magnetic field with magnetic field with magnitude 0.40 T. When you run a 75-A current in the +x direction, you find by careful measurement that the potential at the left side of the slab is 0.81V higher than at the right side of the slab. From this measurement, determine the concentration of mobile electrons in copper.

11 Current carrying wires
1820 Hans Christian Oersted Hans Christian Ørsted

12 Exercise 3 A wire of length l and mass m is suspended as shown. A uniform magnetic field of magnitude B points into the page. What magnitude and direction would a current, passing through a wire, have to have so that the magnetic and gravitational forces would cancel?


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