Understanding the Force on a Current-Carrying Wire in a Magnetic Field
What is a Magnet?
Magnet is a device/object that produces an external magnetic field. It applies force over other magnets, charges, electrical current, and magnetic material. There are several types of magnets. Permanent magnets are the ones which do not lose their magnetism. The majority of the magnets you see are man-made around you. Since they were not initially magnetic, they have lost their magnetic properties over time. For example, dropping them weakens their magnetism. Most of the man-made magnets were originally non-magnetic, and so they lose their magnetic character with time.
What is a Magnetic Field?
The magnetic field is an invisible field around a magnet or magnetic object, in which magnetic force is exerted. The invisible area around a magnetic object can pull up another magnetic object or push away another magnetic object. Moving electric charge generates magnetic fields. A magnetic field can be produced when electrons, which have a negative charge, move about in some certain direction. Magnetic fields can be represented by the continuous line of forces that emerge from the north pole of the magnet and enter into the south pole of the magnet and vice-versa inside the magnet. The density of the lines shows the magnitude of the magnetic field at any point.
Mathematically, the magnetic field can be defined in terms of the amount of force exerted on a moving charge in a magnetic field. This force can be measured with the help of Lorentz Force law,
F = qvB
Where,
F-Force exerted on the moving charge
q-the amount of charge
v-velocity of the moving charge
B-Magnitude of the magnetic field
Here, this relationship is a vector product, and the force is perpendicular to all other values.
Effect of Magnetic Field on a Current-Carrying Wire
Electric energy is transmitted by the current, which is basically the flow of the electrons, which are the sub-particles of the atom and are negatively charged. This movement of electrons from one location to another power our lights, computers, appliances, and many other things. Another fascinating fact about electric current is that it produces its own magnetic field. Magnetism and electricity have a close relation in that all closed-loop currents generate their own magnetic fields, and magnetic fields acting on closed-loop circuits may produce current. The magnetic effect of electric current was discovered by Oersted.
Experiment: How Magnetic Field Affects Current-Carrying Wire?
Materials
Strong horseshoe magnet
Wire stripper
Long insulated wire
Electrical tape
D battery
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Procedure
Remove 1 inch of insulation of the wire from each side.
Place the horseshoe magnet onto a flat surface on its side.
Using a tiny piece of electrical tape to tape the metal portion of one end of the wire through the battery's negative terminal.
Move the horseshoe magnet wire between the legs.
Holding the insulated portion of the wire, connect the wire's open end to the positive battery terminal. What direction is the movement of the electric current? Why do you have to maintain wire insulation instead of metal? List your findings.
Flip over the magnet and repeat the procedure. How, if anything, will change? Document your thoughts.
Results
The wire would bend away from the magnet's poles.
Why this Happens
As we know, electric currents always produce their own magnetic fields. The behavior and the direction of the current can always be described by the right-hand rule. Simply point your thumb towards the direction of current flow, and curl your fingers around the wire, the direction of the curl fingers will give the direction of the magnetic field as shown below in the figure.
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That means you also change the direction of the magnetic field when you change the direction of the current. Magnets have two poles, South and North, like the horseshoe magnet used in this exercise. The term 'attracting opposites' refers to magnets; thus, interactions between north and south hold together, and interactions between north and north and south and south repel or move away from each other.
Fun Facts
The north pole and south pole of a magnet cannot be separated. Cutting one magnet in half makes two magnets, with two poles each.
Earth’s magnetic field is around 1,000 times weaker than the typical bar magnet.
Cranes use huge electromagnets to pick up scrap metal in junkyards.
Electromagnets use electricity to generate their magnetic power. When the electricity is turned on and off, the magnetic power can be turned on and off.
If you attach a bar magnet to a piece of wood and place it in a water bath, it will gradually turn into the water until the North Pole of the magnet points towards the North Pole of our planet. Temporary magnets are used to do the same.
FAQs on How Magnetic Fields Affect Current-Carrying Wires
1. What happens when a wire carrying an electric current is placed in a magnetic field?
When a current-carrying wire is placed inside an external magnetic field, it experiences a mechanical force. This phenomenon, known as the 'motor effect', causes the wire to be pushed or pulled. The direction of this force is determined by the interaction between the magnetic field generated by the current and the external magnetic field.
2. How is the magnitude of the force on a current-carrying wire calculated?
The magnitude of the force (F) on a straight wire in a uniform magnetic field is calculated using the formula F = BILsinθ. The components are:
- F: The force on the wire in Newtons (N).
- B: The strength of the external magnetic field in Tesla (T).
- I: The magnitude of the electric current in Amperes (A).
- L: The length of the wire inside the magnetic field in meters (m).
- θ (theta): The angle between the direction of the current and the magnetic field.
3. How can you determine the direction of the force acting on the wire?
The direction of the force is determined using Fleming's Left-Hand Rule. By arranging the thumb, forefinger, and middle finger of your left hand perpendicular to each other:
- The Forefinger points in the direction of the Magnetic Field.
- The Middle finger represents the direction of the Current.
- The Thumb then points in the direction of the resulting Force or motion.
4. What is a primary real-world application of the force on a current-carrying wire?
The most significant application is the electric motor. In a motor, a current-carrying coil is placed in a magnetic field. The forces on opposite sides of the coil create a rotational effect, or torque, which converts electrical energy into mechanical motion. This principle powers countless devices, including fans, mixers, and electric vehicles.
5. Why does a current-carrying wire experience a force in a magnetic field at all?
The force on the wire is the cumulative effect of the force on countless individual moving charges (electrons) that form the current. A single moving charge experiences a Lorentz force when it moves through a magnetic field. Since the wire contains billions of these moving electrons, the microscopic forces on each charge add up to a significant, observable macroscopic force on the wire itself.
6. What is the crucial difference between the magnetic field *produced by* a wire and the force it *experiences*?
This distinction is fundamental. A wire carrying a current produces its own magnetic field around it, a principle explained by the Right-Hand Thumb Rule. However, it only experiences a force when it is placed within an external magnetic field from another source. The force is the result of the interaction between these two fields, and its direction is found using Fleming's Left-Hand Rule.
7. When is the force on the wire at its maximum, and when is it zero?
The force is at its maximum when the wire is perpendicular (at a 90° angle) to the magnetic field, because sin(90°) = 1. The force is zero if the wire is parallel (at a 0° angle) to the magnetic field, because sin(0°) = 0. In this parallel orientation, the moving charges do not 'cut across' the magnetic field lines, so no force is exerted.
8. How do two parallel wires carrying current exert forces on each other?
Yes, two parallel wires interact because each wire creates a magnetic field that affects the other. The direction of the force depends on the current directions:
- If currents flow in the same direction, the wires experience an attractive force, pulling them together.
- If currents flow in opposite directions, the wires experience a repulsive force, pushing them apart.
9. Besides electric motors, what are some other applications of this force?
Other important applications include the moving-coil galvanometer, used for detecting and measuring small currents, and loudspeakers. In a loudspeaker, a current that varies with the sound signal flows through a coil attached to a cone. This coil is in a magnetic field, and the resulting force makes the cone vibrate, producing sound waves.
10. What happens if the magnetic field is not uniform?
If a current-carrying wire is placed in a non-uniform magnetic field, the force will vary at different points along the wire. Calculating the net force becomes more complex, often requiring calculus (integration) over the length of the wire. Instead of moving as a whole, the wire might experience twisting or stretching forces depending on how the field strength and direction change.
