MIMTY 10/13/10 or 10/14/10 How do you think a power plant generates electricity? MIMTY

Notes on Induction SolenoidsOur lab on solenoids showed us that they have a strong magnetic field running through the center. notes

Notes on Induction SolenoidsOur lab on solenoids showed us that they have a strong magnetic field running through the center. The field is uniform and is easily controllable. But what makes solenoids special? Because they make such a clean magnetic field, they can be used for many interesting things.

Equations Magnetic field of a solenoid equations B = μ 0 I(n/L) B: Strength of the magnetic field in teslas. μ 0 : permeability of free space 1.25×10 -6 mkg /( s 2 A 2 ) I: Current in the wire in amps. n: number of turns in the solenoid. L: length of the solenoid in meters. This equation tells you the strength of a magnetic field inside a solenoid. EVSEVS

Notes on Induction Electromagnetic Induction We’ve learned that moving electricity makes magnetism. However, moving magnetism also makes electricity. The easiest way to create this is by moving a magnet through the inside of a solenoid.

Notes on Induction Electromagnetic Induction We’ve learned that moving electricity makes magnetism. However, moving magnetism also makes electricity. The easiest way to create this is by moving a magnet through the inside of a solenoid. The more powerful the solenoid or faster the movement, the stronger the current!

Notes on Induction Electromagnetic Induction So why don’t we just make solenoids with a billion loops and gets tons of free electricity by pushing a magnet back and forth? The stronger the induced current, the harder it will be to push the magnet through the solenoid.

Notes on Induction Faraday’s Law In 1931, a man named Faraday did many experiments with induction. He came to the following conclusion about the strength of the current: The induced voltage is proportional to the number of loops times the speed at which the magnet moves through the loops.

Notes on Induction Faraday’s Law In 1931, a man named Faraday did many experiments with induction. He came to the following conclusion about the strength of the current: The induced voltage is proportional to the number of loops times the speed at which the magnet moves through the loops. The induced current will depend on the material and resistance of the wire.

Notes on Induction Power Generation Induction is how we generate electricity at power plants.

Notes on Induction Power Generation Induction is how we generate electricity at power plants. The metal loop acts like a simple solenoid. As the loop is turned, the magnetic field going through it changes. This induces an electric current in the wire, generating electricity.

Notes on Induction Power Generation When the loop is perpendicular to the magnetic field, it produces maximum voltage. When parallel, it produces zero voltage.

Notes on Induction Power Generation When the loop is perpendicular to the magnetic field, it produces maximum voltage. When parallel, it produces zero voltage. This is how power plants produce alternating current.

Notes on Induction Power Generation Obviously we don’t hand crank power plants! In coal and nuclear plants, burning coal heats water to boiling. The steam rises and pushes a turbine, cranking the loop.

Notes on Induction Power Generation Obviously we don’t hand crank power plants! In coal and nuclear plants, burning coal heats water to boiling. The steam rises and pushes a turbine, cranking the loop. In a hydroelectric plant, moving water pushes a turbine, cranking the loop.

Notes on Induction TransformersWhen a power plant produces power, it produces at very high voltage. This high voltage is carried through cross-country power lines.

Notes on Induction TransformersWe use a device called a transformer to change the voltage. A transformer is simply two solenoids near each other.

Notes on Induction TransformersWe use a device called a transformer to change the voltage. A transformer is simply two solenoids near each other. If we put a current through “A”, a magnetic field goes through it. That magnetic field also goes through “B”. Making a current go through it too! If the number of loops is different between the 2, we’ll get a different voltage.

Equations Transformer voltage equations v 1 /n 1 = v 2 /n 2 v 1 : voltage in the primary loop n 1 : number of turns in primary loop v 2 : voltage in the secondary loop n 2 : number of turns in secondary loop This equation can be used to calculate the change in voltage from a transformer. EVSEVS

Vocabulary Solenoid Generator Turbine Transformer A coil of wire that induces a magnetic field through it’s center. A device that uses a moving wire or magnet to generate alternating current. A device that moves a wire or magnet to generate electric current. A device that steps up or down the voltage using a pair of linked solenoids. vocab

Induction Review If we place something is the middle of a solenoid, it can decrease or increase its effectiveness. Which material below would increase its effectiveness the most? A)woodB) pencil lead C)skinD) iron E) water

Induction Review Some objects around the house can charge up just by sitting in a charger, without any wires touching. Shown below on the left is a toothbrush that charges this way. If we look inside the base of the toothbrush, we find a solenoid. How does this toothbrush get power? A) From another solenoid in the base B) The solenoid stores power C) It only gets power from the battery D) Electricity goes through the plastic E) The toothbrush doesn’t need power

Induction Review We take a small hand crank generator as shown to the right. If we start spinning the loop inside it faster, what will change? A) The voltage will decrease B) The current will decrease C) The voltage will increase D) The current will increase E) The resistance will increase

Induction Review How many volts would be running through the coil labeled “B”? 200 v, 8 turns ? v, 2 turns “A” “B” A) 0 v B) 25 v C) 50 v D) 75 v E) 100 v

Induction Practice Problems 1)You’re making a solenoid. The wire has 10 A running through it. The solenoid is 2 m long with 200 loops. How strong is the magnetic field inside the solenoid? 2) Why is the wire that makes up a solenoid coated in plastic or cloth? 3)Use what you know about induction to explain how the metal detector at an airport works. 4)Why would a transformer not work if you use DC current? 5)A primary coil in a transformer has 30 turns and carries a 500,000 volts. How many turns should the secondary coil have to step it down to a household voltage of 120 volts?  The device at right shows a solenoid in a donut shape. If we put a magnet inside, why won’t this device be able to generate power for free?  The primary coil of a step-up transformer draws 100 W. Find the power provided by the secondary coil. classwork

Exit Question Why can't we just use 2 solenoids to transmit all power wirelessly?