1. What produces a gravitational field?Mass A gravitational field exerts a force on?Mass What produces an electric field? Electric charge An electric field exerts a force on? Electric charge What produces a magnetic field? Moving electric charge A magnetic field exerts a force on? Moving electric charge?

2. Direction of Magnetic Force Direction of magnetic force is “sideways” çforce is perpendicular to both v and B çuse “right-hand rule” to find direction F = q v B sin  in to page out of page head tail Drawing vectors in

3. A positively charged beam enters into a magnetic field region as shown. What is the direction of B? 1)+ y (up) 2)– y(down) 3)+ x(right) 4)+ z(out of page) 5)– z(into page) ConcepTest Magnetic Force x y

4. Radius of Circular Orbit magnetic force: centripetal accel: Newton's 2nd Law:   This has useful experimental consequences ! x x x x x x x v B +q R F

5. ConcepTest Magnetic Force Two particles of the same charge enter a magnetic field with the same speed. Which one has the bigger mass? x x x x x x A B 1) A 2) B 3) both masses are equal 4) impossible to tell without weighing the particles

6.  s are ionized Helium (bare Helium nuclei) 2-protons, 2-neutrons (positively charged)  s are simply electrons(negatively charged) q  =  2q  m  =7296m 

7.             v= /2Vm/q /B R=?

8. Velocity Selector Consider a positively charged ion entering a region where the electric and magnetic fields are uniform and perpendicular to each other. If the particle moves in a straight line, what is its velocity in terms of E and B? xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx E B For the magnetic force: direction magnitude For the electric force? direction magnitude Sum of the forces on the particle? up F = qvB down F = qE Zero (not accelerating)  |F E | = |F B |  qE = qvB v = E / B

9. xxxxxxxxxxxxxxxxxxxxxxxx Ratio of charge to mass for an electron VV e – “ gun” e–e– R B An electron is accelerated from rest across a potential difference and then enters a region of uniform magnetic field, as shown at right. What is the “charge to mass ratio”, q/m, of the electron? What is the speed of the electron? ½ mv 2 = qV(Work-Energy Theorem) What is the radius of the electron’s orbit? R = mv / qB(Earlier today) Algebra: determine q/m(Solve second Eq for v and plug into first) q / m = 2V / R 2 B 2

10. ConcepTest If all wires carry the same current I, for which of the loops above is the magnitude of the net force greatest? A) Loop 1 B) Loop 2 C) Loop 3 D) same for all 1 23 I I I I

11. A rectangular current loop is in a uniform magnetic field. What direction is the net force on the loop? (a) + x (b) + y (c) zero (d) – x (e) – y ConcepTest Magnetic Force B x z y

12. ConcepTest If there is a DC current in the loop in the direction shown, the loop will A) move up B) move down C) rotate clockwise D) rotate counterclockwise E) some combination of moving and rotating N S

13. a b The force on the top segment of the rectangular loop is 1)up. 2)down. 3)into screen. 4)out. 5)left. 6)right 7)zero.

14. a b The force on the bottom segments of the rectangular loop is 1)up. 2)down. 3)into screen. 4)out. 5)left. 6)right 7)zero.

15. a b The force on the left segment of the rectangular loop is 1)up. 2)down. 3)into screen. 4)out. 5)left. 6)right. 7)zero.

16. a b The force on the right segment of the rectangular loop is 1)up. 2)down. 3)into screen. 4)out. 5)left. 6)right. 7)zero.