Electricity & Magnetism How are electricity & magnetism related?

Warm-up: True or False? Magnets attract all metals. If you cut a magnet in half, one end will be a north pole, the other end will be a south pole. North poles are made of positive electric charges, and south poles are made of negative electric charges.

Conventional Current vs. Electron Flow Electron Flow Model: Electrons flow from the negative terminal to the positive terminal of the source. Conventional Current: From Benjamin Franklin’s Kite Experiment Positive charges were thought to carry current

Relating Electricity & Magnetism When a current flows through the wire, you should have noticed that this causes the needle of the compass to move perpendicular to the wire. Watch This What does this imply?

Oersted’s Discovery Hans Oersted first related electricity and magnetism in 1819 when he noticed that the needle of a compass deflects when placed closed to a current carrying conductor Oersted’s Principle: Electric charges moving through a straight conductor generate a circular magnetic field around the conductor Current flows from positive to negative

Oersted’s Discovery… The field around a straight conductor: Forms concentric circles around the conductor Has a direction that depends on the direction of the current Has a strength that decreases the further you are from the conductor Gets stronger when the current is stronger

Oersted’s Discovery… Cross section of the field around a straight conductor (note how the field weakens further away from the wire): The shaded inner circle represents the cross-section of a straight conductor carrying a current. You can imagine that the X is the tail of an arrow and is moving away from you. This indicates a current that goes into the page. You can imagine that the dot is the tip of an arrow that is facing you. This indicates a current that goes out of the page.

Use right hand rule for a straight conductor How can you predict the direction of the magnetic field around a line conductor? Use right hand rule for a straight conductor Rule is based on the flow of conventional current To apply the rule: Current flows from positive to negative 1. Point your thumb in the direction of conventional current flow 2. Your fingers curl in direction of the magnetic field

Relating Electricity & Magnetism Watch this video until 0:17. What will happen when the switch is pulled? Nothing The wires will always be attracted The wires will always be repelled Sometimes they will attract, and sometimes they will repel

Relating Electricity & Magnetism In the video, what happened when the switch is pulled? When in series, the wires repel When in parallel, the wires attract

Coiled Conductors? Use the right hand rule to predict what the magnetic field will look like in each case. The + and – signs show the direction of conventional current.

Coiled Conductors? Look Here

Coiled Conductors A solenoid is a coiled conductor. The magnetic field created by a current flowing through a solenoid is similar to the field of a bar magnet. Electromagnets are electrically powered bar magnets, that can be turned on and off by turning the current on and off. The field of an electromagnet can be increased by: Increasing the number of loops in the coil Increasing the current Introducing a core made of a material that can be magnetized

How can you predict the direction of the magnetic field produced by a solenoid? Use right hand rule for a solenoid Based on the flow of conventional current To apply the rule: Wrap your fingers in the direction of the conventional current flow Your thumb will point north Current in the coil Number of loops Type of core material (e.g. air, iron…)

Recall: Magnetic Domains Domains in a non-magnetized material Domains in a magnetized material

Strength of an Electromagnet

Magnetic Field of a Solenoid Rank the magnetic field just outside the RIGHT end of the electromagnet from largest to smallest. (Some may be equal.) Explain your ranking!

Magnetic Field of a Loop Magnetic Field of a Series of Loops Hypothesize: Use the right hand rule to predict what the magnetic field will look like in each case. current flow current flow

Homework Pg. 556 #1, 2, 3, 5, 6, 7 Pg. 562 #1, 2, 3, 4, 7 Read and take notes on Pg. 561, “Applications of Solenoids” Really Old School But Cool Video