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$\bullet$ $\cdot$ High-energy cancer treatment. Scientists are working on a new technique to kill cancer cells by zapping them with ultrahigh-energy (in the range of $10^{12}$ W) pulses of light that last for an extremely short time (a few nanoseconds). These short pulses scramble the interior of a cell without causing it to explode, as long pulses would do. We can model a typical such cell as a disk 5.0$\mu \mathrm{m}$ in diameter, with the pulse lasting for 4.0 $\mathrm{ns}$ with an average power of $2.0 \times 10^{12} \mathrm{W}$ . We shall assume that the energy is spread uniformly over the faces of 100 cells for each pulse. (a) How much energy is given to the cell during this pulse? (b) What is the intensity (in $\mathrm{W} / \mathrm{m}^{2} )$ delivered to the cell? (c) What are the maximum values of the electric and magnetic fields in the pulse?

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a)U $=8.0 \mathrm{kJ}$b) $I=1.0 .10^{21} \mathrm{W} / \mathrm{m}^{2}$c) $B_{\text {max}}=2.9 .10^{3} \mathrm{T}$

Physics 102 Electricity and Magnetism

Physics 103

Chapter 23

Electromagnetic Waves and Propagationof Light

Electromagnetic Waves

Reflection and Refraction of Light

Rutgers, The State University of New Jersey

Hope College

University of Sheffield

Lectures

02:30

In optics, ray optics is a geometric optics method that uses ray tracing to model the propagation of light through an optical system. As in all geometric optics methods, the ray optics model assumes that light travels in straight lines and that the index of refraction of the optical material remains constant throughout the system.

10:00

In optics, reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected. Reflection may also be referred to as "mirror image" or "specular reflection". Refraction is the change in direction of a wave due to a change in its speed. The refractive index of a material is a measure of its ability to change the direction of a wave. A material with a higher refractive index will change the direction of a wave to a greater degree than a material with a lower refractive index. When a wave crosses the boundary between two materials with different refractive indices, part of the wave is refracted; that is, it changes direction. The ratio of the speeds of propagation of the two waves determines the angle of refraction, which is the angle between the direction of the incident and the refractive rays.

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All right. So in this medical experiment, we know that Ah, for this laser, the power is Pequot two times 10 to the 12th. What's and lasting time is for nanoseconds so in part. And we're gonna figure out that the energy equal p times t great, and this gives you eight times 10 to the third. Jos. Sorry. Third Joe's okay. And in part B. So we're gonna find out intensity on the sale. So basically, we model each cell as a disc in this case, okay? And the and the diameter of the did it off the disc is five micrometers. So, uh, for for each sale. The power that I received from the laser is a small p equal total p over 100 because the laser is shedding on the 100 sales. So this gives you two times into the tens, Moz. And the intensity on the sale equal smoky over ass where ass is the area of the disc. So, uh, this also equal p over pi are squid. Where are these? The diameter Over too. So you've been plugging the vet use and you see that this that is 1.1 times 10 to the 21st Waltz Meter squared, Okay. And in Parsi. So we want to find out to the magnitude of the magnetic field. Ah, winning a relation between the intensity and the magneto and the magnitude of the Electra feud is half see, Time's up. So not E max squid. And also the be max, which is the magnitude of the magnetic field. Can you attend by the magnitude Electra feud over See where c is the speed of light and absolute is the electric constant. So if you're plugging the veggies and you see that the be Max here equal 2.9 times 10 to the third Tesla, okay?

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