Download presentation

Presentation is loading. Please wait.

1
Magnetic Field PH 203 Professor Lee Carkner Lecture 15

2
HRW 7 Ed., P 27.20 Junction rule (at point d) i 1 +i 3 =i 2 Left loop: Right loop: Solve loop rule in terms of common variable, i 3 i 1 = ( 1 +i 3 R 3 ) / R 1 i 2 = (- 2 -i 3 R 3 ) / R 2 Put in numbers i 2 = -0.1 – 0.5i 3 1 = 4 V 2 = 1 V R 1 = 10 R 2 = 10 R 3 = 5

3
HRW 7 Ed., P 27.20 Put in loop rule i 1 +i 3 =i 2 0.4 + 0.5i 3 + i 3 = -0.1 – 0.5i 3 2i 3 = -0.5 A i 3 is drawn backwards i 1 = 0.275 A These are drawn right V d –V c = i 2 R 2 = (0.025)(10) = +0.25 V 1 = 4 V 2 = 1 V R 1 = 10 R 2 = 10 R 3 = 5

4
HRW 7 Ed., P 27.26 Power input to circuit is i V = Power dissipated by each resistor is i 2 R Voltage across A and B must equal voltage of 2 and 6 resistors i 1 = [78 – (6)(6)]/2= 21 A Junction rule i 1 = i 2 + i i 2 = 21 – 6 = 15 A i = 6 A V A -V B =78 V i1i1 i2i2

5
HRW 7 Ed., P 27.26 Power input to circuit: Power dissipated by all resistors (i 2 R each): Since the resistors are using 1998 W and the applied voltage only supplies 1638 W, the box must be providing: 1998 – 1638 = 360 W i = 6 A V A -V B =78 V i1i1 i2i2

6
Electricity and Magnetism Magnets exert a force on two types of objects: Both of these forces are due to the same fact: Magnetic fields produce a force on moving charges Moving charges produce a magnetic field Both electricity and magnetism are related to charge

7
Vectors A magnet produces a magnetic field (B) The moving particle has a velocity (v) All three quantities are vectors What is the relationship between them? i.e., if the B field points one way and the charge is moving another way, what is the direction of the force?

8
Right Hand Rule If v is your straight fingers, and you curl your fingers in the direction of B, F is your thumb F v B

9
Vector Conventions The force on a negative particle is opposite that of a positive one Vectors going into the page are represented with a cross (X), vectors going out of a page are represented with a dot ( )

10
Magnetic Force Magnitude The magnitude of the magnetic force depends on 4 things: The magnitude of the charge (q) The angle between the v and B vectors ( ) The force can be written as: F = qvB sin

11
Charged Particle in Field q v B

12
Magnetic Field We can use the expression for the force to write an expression for the magnetic field: B = F/qv sin We will often use a smaller unit, the gauss (G) Typical bar magnet ~ Earth’s magnetic field ~

13
Crossed Fields Electric force: in direction of field If the E and B field are at right angles to each other, the forces will be in opposite directions

14
Velocity Selector How could we get the forces to cancel out? If we “tune” B until the particle is not deflected, we can find the velocity

15
Next Time Read 28.6-28-10 Problems: Ch 28, P: 9, 15, 16, 32, 46

16
A resistor R and capacitor C are connected to a battery. If the resistor is replaced with a resistor of 2R, what happens to the time needed to charge the capacitor? A)It increases B)It decreases C)It depends on C D)It stays the same E)None of the above

17
Over which time range does the charge on a capacitor increase the least (t=0 is uncharged) A)0 to 1 B)1 to 2 C)2 to 3 D)3 to 4 E)4 to 5

18
Consider a simple circuit consisting of a battery and resistor. What will happen to the current if a voltmeter is used to measure the voltage through the resistor? What will happen to the current if a ammeter is used to measure the current through the resistor? A)increase, increase B)increase, decrease C)decrease, decrease D)decrease, increase E)You can’t tell without knowing the voltage of the battery

Similar presentations

© 2021 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google