Magnetic Force and Field Magnetic Poles Every magnet
- Slides: 23
Magnetic Force and Field
Magnetic Poles Every magnet has two poles (North & South) and is therefore called a Dipole Unlike Electric Fields it is impossible to have a Monopole. If you cut a magnet in half you end up with another dipole. N S S N N S Unlike poles attract, Like poles repel. S N N S S N These magnets will turn so that UNLIKE poles come together. N S
Earth’s Magnetic Field Because magnets will turn so that UNLIKE poles come together, the poles are really called ‘North seeking poles’ or ‘South seeking poles’ Compasses contain small magnets which turn towards the Earth’s poles. N S http: //phet. colorado. edu/en/simulation/magn ets-and-electromagnets
Magnetic Field Lines Magnetic Field This is a region of space where a test magnet experiences a turning force http: //www. walter-fendt. de/ph 14 e/mfbar. htm Field Lines They point from the North Pole to the South Pole.
Magnetic Flux Density (B) The strength of the magnetic field seems linked to the density of the magnetic field lines. There is a stronger field at the poles where there are more field lines. Magnetic Flux Density (B) This is the equivalent of: g for Gravitational Fields (Nkg-1) E for Electric Fields (NC-1) The unit of Magnetic Flux Density (B) is the Tesla (T) and like the other field strengths it is a Vector. A good way to think about it is that it is just a measure of how many Field Lines there are in a certain area. A magnetic field is often called a ‘B Field’ Until we know more about Magnetism it isn’t possible to define The Magnetic Field Density (B) in the same way as we do for Gravitational Field Strength (g) and Electric Field Strength (E)
Fields Caused by Currents It turns out that if a small compass is placed near a wire carrying a current it experiences a weak turning force. This led scientists to that Magnetism is caused by moving charges. The field is strongest closest to the wire. The direction of the field can be found using the Right Hand Corkscrew Rule. http: //www. walterfendt. de/ph 14 e/mfwire. htm realise actually The fingers show the direction of the field.
Field inside a coil When a current flows around a circular loop the magnetic field forms circles. All these circles add together. This makes a really strong field in the centre of the circular loop.
Field inside a solenoid A solenoid is a coil of wire, carrying a current. The field that is created by a solenoid is just like that of a bar magnet but the field lines go through the centre.
Force on a current carrying conductor review
Changing the direction of the force review The direction of the force acting on a wire in an electromagnetic field can be reversed by: Reversing the Current Reversing the Magnetic Field The direction of the force is therefore relative to both the direction of the magnetic field and the current.
Fleming’s left-hand rule review It is possible to predict the direction of the force acting on a wire – its motion – if the direction of the current or the magnetic field are known. Fleming’s left-hand rule is used to do this. thu. Mb = Motion First finger = magnetic Field se. Cond finger = Current
Increasing the size of the force review
Force in a Magnetic Field equation As you have just seen the size of the force depends on: B – Magnetic Flux Density I – current in the wire l – length of wire If the field is not at Right Angles to the wire then the perpendicular component of the field is used and the equation is:
Force in a Magnetic Field alternative equation B – Magnetic Flux Density I – current in the wire l – length of wire 1. 2. 3. 4.
Charges in Magnetic Fields 1. Electrons moving in a wire . = B Field coming out of page ⨯= B Field going away into page Imagine an arrow coming towards you or going away from you. In the picture above, the electron is moving to the right, so Conventional Current (I) is moving to the left. From Fleming’s Left Hand Rule the electron experiences a force downwards at right angles to it’s motion. It’s the sum of all the forces on all the electrons that gives the total force on the wire. 2. Electrons moving freely through a magnetic field The force is always perpendicular to it’s motion, so it ends up moving in a circle. The Magnetic Field provides the Centripetal Force.
What forces are there between two current carrying wires? Step 1 – What does I 2 do to I 1 ? Use the Right Hand Corkscrew rule to see what the field lines do. Step 2 – Which way does I 1 move? Use Fleming’s Left Hand Rule to see what the force is on I 1 F
Now repeat for the other wire: Force caused by I 2 on I 1 Force caused by I 1 on I 2 F F The two wires move together!
If the currents are flowing in opposite directions: I I If the currents are flowing in opposite directions:
What would happen to a coil? What happens to the shape of the coils?
What would happen to a coil? http: //ocw. mit. edu/ans 7870/8/8. 02 T/f 04/visualizations/magnetostatics/15 -Magnetic. Force. Attract/Mag. Force. Att_640. mpg
Aurora Borealis Knut Birkeland (1867– 1917) is on the 200 Norwegian kroner note. He was a Physicist best known for his studies on the aurora borealis. Timelapse of the Aurora http: //vimeo. com/16917950
Aurora Borealis – the Physics The Earth has a magnetic field caused by currents in its core, which channels charged particles from solar flares and from our upper atmosphere towards the poles
Aurora Borealis – the Physics Charged particles from space experience a force on them from the earth’s magnetic field which makes them spiral around the magnetic field lines and head towards the poles. As they meet air molecules they excite the molecules causing them to give out light. Without the protection of the earth’s magnetic field we would be constantly bombarded with high energy particles. This is one of the reasons that Space flight is so difficult. Astronauts report white flashes in their vision as Cosmic rays pass straight through their heads. Without shielding missions to Mars will be impossible.
- Force on a charged particle
- Magnetic field lines that curve away from each other show
- A wire suspended vertically between the poles of a magnet
- Magnetic field lines of a bar magnet
- Cow magnet magnetic field
- A magnetic force
- Horseshoe magnet magnetic field
- Magnetic moment and magnetic field relation
- Magnetic field strength formula
- Gauss law of magnetism
- Distinguish between magnetic and nonmagnetic materials
- Difference between electric field and magnetic field
- How do magnetic poles interact?
- How do similar (s-s or n-n) magnetic poles interact?
- Characteristics of magnetic field
- What happens if you break a magnet in half
- Permanent and temporary magnet
- Right hand rule for electron in magnetic field
- Facts about magnetic forces
- Does magnetic field exerts force on a static charge
- Electric force equation
- Does magnetic field exerts force on a static charge
- Force exerted by magnetic field
- Kedudukan magnet elementer di dalam sebuah magnet adalah