𝐵 ⊥ is the field component perpendicular to A. Magnetic flux () is a measure of how much magnetic field is passing through a loop of wire. It is at a maximum when the field lines are perpendicular to the plane of the loop, and it is zero when the field lines are parallel to the plane of the loop. For a coil of N loops, the flux through the coil is equal to the flux through one loop, multiplied by the number of loops: 𝜙=𝑁∙ 𝐵 ⊥ ∙𝐴 𝐵 ⊥ is the field component perpendicular to A.

Faraday’s Law A voltage (electromotive force) is induced in a circuit when there is a changing magnetic flux passing through the circuit. The induced voltage is equal to the rate of change of the magnetic flux: This process is called electromagnetic inductance.

How to use Faraday’s law to determine the induced current direction determine the sign of ∆Φ. Here ∆Φ >0 determine the sign of  using faraday’s law. Here  <0 RHR determines the positive direction for EMF  Align you thumb approximately to the field direction. If >0, current follow the direction of the curled fingers. If <0, current goes to the opposite direction of the curled fingers. N

Conducting Loop in a Changing Magnetic Field Induced EMF has a direction such that it opposes the change in magnetic flux that produced it. approaching moving away Now the demonstration again Magnetic moment  created by induced currrent I attracts the bar magnet. Magnetic moment  created by induced currrent I repels the bar magnet. Force on ring is attractive. Force on ring is repulsive.

Exercise The magnetic field is increasing, what’s the direction of the induced currents in the closed circular loop? Clockwise Counterclockwise No induced currents. Then go to the jumping ring.

6D-11 Jumping Ring Is there any differences in the two rings ? Why one can jump up, the other can’t ?

Inductor Radio (6D-15) Two separate coiled conducting loops are used in this demonstration. One loop is connected to a radio tuned to a station. The other loop is connected to a speaker. The loop connected to the radio will transmit a signal that induces a magnetic field created by the current in the loop. The signal is received in the speaker loop which induces an electric current in the wire which will drive the speaker and emit the sound.

Electric Generator Model (6B-16) This is a demonstration of an electric generator, an electromechanical device which converts mechanical energy to electrical energy. This model operates on the interaction of a conducting loop spinning in a magnetic field. A current is generated when the armature coil is forced to spin.

UHF Transmitter and Dipole Receiver (6D-17) Directions for doing the demo: Before powering the transmitter select the operating mode with the mode switch (preferably CW – continuous wave). Turn on the power to the transmitter. Move the receiver dipole close to the transmitter. The intensity of the lamp indicates the field strength of the signal. Move the receiver farther away and the light intensity diminishes. Rotate the receiver 90 degrees and the light goes out completely. Connect the receiver antenna to a voltmeter and you will get numerical readings indicating field strength of the signal.

The Existence of Atoms: Evidence from Chemistry Why believe in the existence of something we have never seen? Observations can provide convincing evidence. Much early evidence of atoms came from chemistry, the study of the differences in substances and how they can be combined to form other substances. Since certain substances were retrievable, early scientists were also tempted to believe that certain elements were made up of tiny indivisible atoms.

Cathode rays, Electrons, and X-rays By the end of the nineteenth century, chemists were using the concept of atoms to explain their properties. Physicists were less convinced. The discovery of cathode rays was the beginning of atomic physics. Two electrodes are sealed in a glass tube. As the tube is evacuated, a glow discharge appears in the gas between the electrodes. With further evacuation, the discharge disappears, and a glow appears on the end of the tube opposite the cathode. Coat the tube with phosphorescent

Thomson’s discovery provided the first known subatomic particle. The mass of an electron is 9.1 x 10-31 kg. The charge of an electron is 1.6 x 10-19 C. The electron was the first possible candidate for a building block of atoms. The study of cathode rays led Roentgen to discover yet another type of radiation.

Cathode rays could not travel through air, but this new radiation did. He noticed that a fluorescent material would glow when placed near his covered cathode-ray tube. Cathode rays could not travel through air, but this new radiation did. Because they were unknown, Roentgen called this new radiation X-rays. 1st Nobel Prize Winner Wikipedia: “print of Roentgen’a first "medical" X-ray, of his wife's hand, taken on 22 December 1895”

Rutherford noticed when the beam of radiation from a uranium sample passes through a magnetic field, it splits into three components. Alpha deviates slightly to the left, indicating positively charged particles. Beta is bent in the opposite direction, indicating negatively charged particles. Beta is also bent much more, indicating less massive particles than those in the alpha beam. Further study indicated that these beta rays were electrons. 𝐹=𝑚𝑎= 𝑚 𝑣 2 𝑟  𝑟=𝑚 𝑣 2 /𝐹 The gamma rays were undeviated by the magnetic field. These are electromagnetic waves similar to X-rays but with shorter wavelengths. Use right hand rule to demonstrate the magnet force.