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1. You are given a number of 10 omega resistors, each capa-ble of dissipating only 1.0 W without being destroyed. What is the minimum number of such resistors that you need to combine in series or in parallel to make a 10 omega resistance that is capable of dissipating at least 5.0 W? 

2. A proton traveling at 23.0 degrees with respect to the direction of a magnetic field of strength 2.60 mT experiences a magnetic force of 6.50x10^-17 N. Calculate (a) the proton's speed and (b) its kinetic energy in electron-volts. 

For #2, I got 400 km/s in part (a) and I think the formula for part (b) is 1/2mv^2 and I plug 1.67x10^-27 kg for m and 400 km/s for v but I didn't get the correct answer, it should be 835 eV. Do I need to convert something?

Pingu · Accepted Answer

Nine.

If we put three 10 Ω, 1W resistors in parallel, the resistance is given by

1/𝑹 = 1/R₁ + 1/R₂ + 1/R₃ = 3/10

𝑹 = 3.33 Ω

If we put three of these constructions in series, then the net Resistance is 10 Ω, and 9 W can be dissipated.

……………………………………

A series construction of two sets of two resistors in parallel would also give a net resistance of 10 Ω, but the power dissipation would only be 4 W.

iron-side · Answer

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