Ampère's Law: Crash Course Physics #33

CrashCourse
8 Dec 201608:45
EducationalLearning
32 Likes 10 Comments

TLDRIn 1820, Hans Christian Oersted discovered the connection between electricity and magnetism. Around the same time, French physicist André-Marie Ampère was experimenting with wires to understand the relationship between electric currents and magnetic fields. He found that parallel wires with currents flowing in the same direction attract each other, while wires with opposite currents repel. Studying these phenomena led Ampère to formulate Ampère's Law, relating the magnetic field around a loop enclosing an electric current. He also found that a coil of current-carrying wire can act like a magnet, and that a current loop in a magnetic field will rotate. These principles help explain how electric motors work in various appliances we use every day.

Takeaways
  • 😲 Ampère discovered that parallel wires with current flowing in the same direction attract each other, while wires with current flowing in opposite directions repel each other
  • 👨‍🔬 Ampère's law relates the magnetic field around a closed loop to the electric current passing through the loop
  • 📏 For a long straight wire, the magnetic field strength at any point on a circle surrounding it depends on the current and the circle's radius
  • 🔀 The direction of the magnetic field created by a current-carrying wire can be found using the right-hand rule
  • 🧲 When wrapped into a coil, a current-carrying wire creates a magnetic field similar to a bar magnet
  • ⚡ The number of coils in a solenoid determines the strength of the magnetic field inside it
  • 🔁 When a current-carrying coil is placed in an external magnetic field, it experiences a torque that makes it rotate
  • 🤯 Ampère's discoveries helped explain how motors convert electric current into mechanical work
  • 💡 Electric motors power many common appliances like washing machines, drills and computer fans
  • 🙌 We have Ampère to thank for enabling much of our modern electrically-powered world
Q & A
  • What connection did Hans Christian Oersted discover?

    -Hans Christian Oersted discovered the connection between electricity and magnetism.

  • What did André-Marie Ampère discover through his experiments with parallel wires?

    -Through his experiments, Ampère discovered that parallel wires carrying current attract each other when the current flows in the same direction and repel each other when the current flows in opposite directions. This led him to formulate Ampère's law.

  • What is Ampère's law and what does it state?

    -Ampère's law states that the integral of the magnetic field B along a closed loop is equal to the permeability constant mu_0 times the electric current passing through the loop. It relates the magnetic field around an electric current to the magnitude of the current.

  • Why does a current-carrying coil act like a magnet?

    -When electric current flows through a coil, it generates a magnetic field inside the coil, with a north pole at one end and south pole at the other, making it act like a magnet.

  • Why does a current-carrying loop rotate when placed inside a magnetic field?

    -The magnetic field exerts a force on the vertical sections of the loop perpendicular to the field, creating a torque that causes the loop to rotate.

  • How do motors work based on the principles described?

    -Motors have loops of wire carrying alternating electric current. This causes the loops to continuously rotate due to the torque created by the magnetic fields, allowing them to do mechanical work.

  • What causes parallel wires with current flowing in the same direction to attract each other?

    -The magnetic fields created around each wire due to the current point toward each other, causing an attractive force between the wires.

  • What is the direction of the magnetic field created around a current-carrying straight wire?

    -The magnetic field circles around the wire perpendicular to it, as given by the right-hand grip rule for magnetic fields around a wire.

  • What is the magnitude of the magnetic field along a circular loop around a straight current-carrying wire?

    -B = (mu_0*I)/(2*pi*r) , where I is the current and r is the radius of the circular loop.

  • Who do we have to thank whenever we use devices with electric motors?

    -We have André-Marie Ampère to thank for discovering the relationship between electricity and magnetism through experiments with current-carrying wires, which led to our understanding and applications of electric motors.

Outlines
00:00
🧲 Ampère Discovers Relationship Between Electricity and Magnetism

This paragraph provides background context, describing how in 1820 Hans Christian Oersted discovered the connection between electricity and magnetism. It then introduces Ampère, a French physicist who was also studying this phenomenon by experimenting with parallel wires carrying electric currents. Ampère found that wires with currents flowing in the same direction attract each other, while wires with opposite currents repel, leading him to discover Ampère's Law relating electric current and magnetic fields.

05:02
👉 Ampère's Law and Magnetic Fields

This paragraph explains Ampère's Law - the mathematical relationship between the magnetic field around a loop and the electric current passing through it. It describes how the strength of the magnetic field is proportional to the enclosed current. The paragraph then applies Ampère's Law to the specific example of a long straight wire, deriving the equation for the magnetic field along a circular loop around the wire.

😲 Forces Between Wires and Electromagnets

This paragraph applies Ampère's Law to explain the attraction and repulsion forces between parallel wires carrying current. It uses the right-hand rule to illustrate why wires with current in the same direction attract, while opposite currents repel. It then explains how coiling wire into a solenoid shape creates a strong internal magnetic field, turning the coil into an electromagnet. The number of coils intensifies the magnetic field strength according to Ampère's Law.

⚡ Motors and Applications of Electromagnetism

The final paragraph describes what happens when a wire loop is placed in a magnetic field - it rotates due to the torque exerted by the field. This phenomenon is harnessed in electric motors, allowing mechanical work to be done. The paragraph concludes by highlighting the ubiquity of electric motors in modern life, emphasizing Ampère's pioneering role in understanding electromagnetism.

Mindmap
Keywords
💡electromagnetism
Electromagnetism refers to the interrelationship between electricity and magnetism. It is a fundamental concept in physics that describes how electric currents and magnetic fields influence each other. In the video, this concept is introduced through the discovery of the connection between electricity and magnetism by Hans Christian Oersted and André-Marie Ampère in the early 1800s.
💡current
Electric current refers to the flow of electric charges in a conductor. The video explains how electric currents generate magnetic fields around them. For example, the current running through a wire creates a circular magnetic field around it. The strength of the magnetic field depends on the amount of current flowing through the wire.
💡Ampere's Law
Ampere's Law describes the relationship between electric current and the magnetic field it generates. It states that the magnetic field around a closed loop is proportional to the amount of current passing through the loop. Ampere derived this law by experimenting with parallel wires carrying electric current and observing how they interacted.
💡magnetic field
A magnetic field is the region surrounding a magnet or electric current where magnetic forces can be detected. The video discusses how electric currents produce circular magnetic fields around them. The strength and direction of these fields can be determined using Ampere's Law and the right-hand grip rules.
💡solenoid
A solenoid is a coil of wire in the shape of a cylinder. When electric current passes through a solenoid, it generates a strong magnetic field through the center of the coil. Ampere's Law can be used to calculate the magnetic field strength inside a solenoid based on its number of loops and the amount of current.
💡torque
Torque is a rotational force that produces rotation. In the video, a loop of wire carrying electric current placed in a magnetic field experiences a torque. This happens because the magnetic field exerts a force on different sections of the wire loop, causing it to rotate. This torque principle allows electric motors to spin and do mechanical work.
💡electric motor
An electric motor uses electric current and magnetic fields to produce rotational motion. Electric motors contain loops of wire that spin when electric current is run through them in a magnetic field. As explained in the video, this torque effect was discovered by Ampere and is key to how electric motors convert electrical energy into kinetic energy.
💡electromagnet
An electromagnet is a magnet powered by electric current rather than permanent magnetism. When electric current flows through a coil of wire, it creates a magnetic field just like a regular magnet. Electromagnets can be turned on and off by controlling the electric current. Solenoids and electric motors contain electromagnets.
💡right-hand rules
The right-hand rules, or grip rules, are techniques used to determine the direction of magnetic fields generated by electric current. As demonstrated in the video, curling the fingers of the right hand around a wire signifies the magnetic field direction. Pointing the thumb in the current's direction indicates the force acting on the wire.
💡integral
An integral sums up the area under a curve representing a function. Integrals are used in Ampere's Law to calculate the total magnetic field along a loop surrounding a current. The video explains how the integral accounts for contributions from the entire loop encircling the electric current.
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Transcripts
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