319K/H SI Week 5 - ECE 302 Review

There is 1V and 5mA across a resistor. What is the resistance?

• 0.2Ω

• 200Ω

• 2kΩ

• 20kΩ

Answer explanation

Ohm's Law R=V/I = 1V/0.005A = 200Ω.

There is 2V across a 100Ω resistor. How much current is flowing?

• 20mA

• 200A

• 50mA

• 50A

Answer explanation

Ohm's Law I=V/R = 2V/100Ω = 20mA.

What happens if you place a wire directly from the + terminal to the - terminal of a battery?

• Nothing

• Recharge battery with itself

• Theoretically infinite current and BOOM!

• Theoretically infinite voltage and BOOM!

Answer explanation

Theoretically, the current will be infinite, but practically there will be sparks.

There is 1V across a resistor, and 5mA is flowing. How much power is being dissipated?

• 200W

• 5mW

• 25uW

• Not enough information - need resistance

Answer explanation

Power is V*I = 1V*0.005A = 5 mW.

Which of these statements is true?

• Voltage is the same in series, current is the same in parallel

• Current is the same in series, voltage is the same in parallel

• Both are the same in series

• Both are the same in parallel

Answer explanation

Remember KVL and KCL! This is important for measuring with a multimeter!

There is 2V across a 100Ω resistor. How much power is being dissipated?

• 50W

• 200W

• 2mw

• 40mW

Answer explanation

Power is V²/R = 2V*2V/100Ω = 40 mW.

The term used to define the amount of work that can be done. Units are in joules (J).

• Power

• Current

• Energy

• Voltage

Answer explanation

Because the laws of physics, all types of energy are defined in joules, and it is actually describing the same thing. So, for example, the newton-meter in mechanics is equivalent to the watt-second in electronics! :-)

If a battery has 0.81W and 1000J, how long will the light be illuminated, assuming the voltage is constant?

• 1234 seconds (~21 minutes)

• 8100 seconds (135 minutes)

• 656 seconds (~11 minutes)

• Not enough information

Answer explanation

Energy is power*time, so 1000J = 0.81W*t(in sec), so t = 1000/0.81=1234 sec, which is about 20 minutes.

Using the following image, assume I=1mA, R1=2kΩ, R2=3kΩ. What is V? Type only the number.

Answer explanation

Use the voltage divider rule. Total resistance is 2kΩ +3kΩ = 5kΩ. Ohm's Law V=I*R = 0.001A*5000Ω = 5V.

Use the following image. Assume V is 10V, R1 is 2kΩ, and R2 is 4kΩ. What is I2 in mA? Type only the number.

Answer explanation

Use the current divider rule. Ohm's Law I₂=V/R₂ = 10V/4000Ω = 2.5mA.