Moving Charges in Magnetic Fields Topic 12.2 & 12.3

Outcomes You will define electric current as the amount of charge passing a reference point per unit of time You will explain, qualitatively and quantitatively, how a uniform magnetic field affects a moving electric charge, using the relationships among charge, motion, field direction and strength, when motion and field directions are mutually perpendicular You will describe and explain, qualitatively, the interaction between a magnetic field and a moving charge and between a magnetic field and a current-carrying conductor You will explain, quantitatively, the effect of an external magnetic field on a current-carrying conductor

What is current? Electric current is the rate of flow of electric charge (electrons) When electrons move, they can posses energy and do work

Sample Problem I = 5.00A (or 5.00C/s) Calculate the current in a wire through which 20.0C of charge passes in 4.0s. I = 5.00A (or 5.00C/s)

Types of Current There are two kinds of current: NO VOLTAGE, NO FLOW Conventional Current: Positive charges move as a result of a potential difference (from + to – terminal) Electron Flow: Electrons flow as a result of a potential difference (from – to + terminal) NO VOLTAGE, NO FLOW

Current Carrying Conductor in a Magnetic Field A current carrying conductor will experience a force when placed in an external magnetic field A wire with a current will produce its own magnetic field Moving charges produce magnetic fields This field interacts with the external magnetic field producing a force on the wire

HAND RULE #3 Predicts the direction of the force on a current carrying conductor (or charge particle) moving in an external magnetic field. Using an open hand, the Thumb – direction of the current in the conductor Fingers - direction of the external permanent magnetic field Palm – direction of the force on the wire

Homework Concept Q’s: p. 601 # 3 – 5 p. 56 #13 – 22 (workbook) 20 & 21 may require some explanation….

Day #2 – Calculating Magnetic Forces

Force on a Current Carrying Wire The magnitude of the force on a Current Carrying Wire can be calculated using the formula:

Sample Problem Fm = 7.50x10¯⁴ N (upwards) An 8.50cm length of conducting wire lies perpendicular to an external magnetic field of magnitude 4.20mT, as shown in the figure below. If there is a negative charge flow of 2.10A in the conductor, calculate the magnetic force on the wire. Fm = 7.50x10¯⁴ N (upwards)

Moving Charges in Magnetic Fields The magnitude of the deflecting magnetic force (on a moving charge) can be calculated using:

Important Points!!! If a particle is moving parallel to a magnetic field, THERE IS NO FORCE on the particle due to the magnetic field The third hand rule also applies to moving particles in a magnetic field If the magnetic field the charge enters is large, the particle may be forced to travel in a circular path

Sample Problem 1.3x10¯¹⁴ N (upwards) An electron is travelling at 3.20x10⁵m/s perpendicular to an external magnetic field of magnitude 2.20x10¯¹ T. Determine the magnetic force acting on the electron. 1.3x10¯¹⁴ N (upwards)

Homework Concept Q’s: Calculation Q’s: p.613 #1,2,8,9 p.601 # 6a). – 10 p.74 #2 – 12 even (workbook)