Chris Johnson

Sonoma State University
Science Department Chair; Physics and Astronomy Teacher

Biography

I have always been facinated by science, especially Astronomy and Physics. I went to Sonoma State for my undergraduate degree in Astrophysics, and from there went to San Francisco State for my Masters. While there, I became quite ill, and had to move back home. However, it was during this period of time where I really started to get into teaching. I then got my teaching credential, and started teaching High School. I have been teaching at the Army and Navy Academy in Carlsbad Ca, for 6 years. During that time I have also become the department chair for science and computer science. Outside of the pure academic realm, I host twitch streams where people can just ask random science and astronomy questions, and I try and teach people! Science is amazing, fun, and not nearly as difficult as it first seems. I hope to be able to share that with students on here.

Education

BA Astrophysics
Sonoma State University

Educator Statistics

Numerade tutor for 6 years
143 Students Helped

Topics Covered

Relativity
Calculating Electrical Power: Resistance and EMF
Master Direct Current Circuits with Our Expert Guide
Electromagnetic Induction: Understanding the Science and Applications

Chris's Textbook Answer Videos

05:21
Physics for Scientists and Engineers with Modern Physics

A battery has an emf of 15.0 V. The terminal voltage of the battery is 11.6 V when it is delivering 20.0 W of power to an external load resistor R. (a) What is the value of R ? (b) What is the internal resistance of the battery?

Chapter 28: Direct-Current Circuits
Chris Johnson
04:33
Physics for Scientists and Engineers with Modern Physics

Two $1.50-\mathrm{V}$ batteries - with their positive terminals in the same direction-are inserted in series into a flashlight. One battery has an internal resistance of $0.255 \Omega,$ and the other has an internal resistance of 0.153 . When the switch is closed, the bulb carries a current of 600 $\mathrm{mA}$ .

Chapter 28: Direct-Current Circuits
Chris Johnson
04:28
Physics for Scientists and Engineers with Modern Physics

An automobile battery has an emf of 12.6 $\mathrm{V}$ and an internal resistance of 0.0800$\Omega$ . The headlights together have an equivalent resistance of 5.00$\Omega$ (assumed constant). What is the potential difference across the headlight. bulbs (a) when they are the only load on the battery and
(b) when the starter motor is operated, requiring an additional 35.0 A from the battery?

Chapter 28: Direct-Current Circuits
Chris Johnson
01:54
Physics for Scientists and Engineers with Modern Physics

As in Example 28.2, consider a power supply with fixed emf e and internal resistance r causing current in a load resistance R. In this problem, R is fixed and r is a variable. The efficiency is defined as the energy delivered to the load divided by the energy delivered by the emf. (a) When the internal resistance is adjusted for maximum power transfer, what is the efficiency? (b) What should be the internal resistance for maximum possible efficiency? (c) When the electric company sells energy to a customer, does it have a goal of high efficiency or of maximum power transfer? Explain. (d) When a student connects a loudspeaker to an amplifier, does she most want high efficiency or high power transfer? Explain.

Chapter 28: Direct-Current Circuits
Chris Johnson
02:00
Physics for Scientists and Engineers with Modern Physics

What is the equivalent resistance of the combination of identical resistors between points $a$ and $b$ in Figure $\mathrm{P} 28.5 ?$

Chapter 28: Direct-Current Circuits
Chris Johnson
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