1. When an ohmmeter is used to test a diode, a very low resistance (but not zero) in one direction means that?

Question

the diode is a. open b. forward c. shorted d. reversed bias

2. for which region the diode curve look like an open circuit

a. diode voltage less thatn the barrier potential

b. diode voltage greater than the barrier potential

3. for the region of the diode curve greater than the diode's barrier potential

a. the curve is essentially horizontal

b. the diode forward resistance approaches an open circuit

c. the diode voltage increases rapidly

d. the diode current increases

Answer 1

1. b; if open the resistance would be infinite, if shorted the resistance would be zero, (theoretically, but in reality there would be some resistance, so we can't positively say c is not the answer, but I'm pretty sure b is the intended answer), if reverse biased the resistance would be very high

2. a; If the voltage were more that the barrier potential it would look more like a short (but not quite) than an open

3. d; as above, if the voltage is higher than the barrier potential it looks like a low resistance, so the current increases.

Answer 2

1/  b) forward biased diode appears as a low resistance

2/ a) when the diode  voltage is less than the barrier voltage, the diode doesn't conduct (appears as an open circuit

3/ d) After the barrier voltage is exceeded, the diode behaves like closed switch - it's current increases dramatically.

Think about the I-V characteristic curve for a diode.  At voltages close to zero, the current is zero.  At some voltage (.5V - 2.2V depending on the device), the current will increase until it appears to be a sloped line.

Of course, when voltage increases beyond the device's maximum rating, the diode will explode and current will drop to zero. To demonstrate, try putting 120V across a 1n... diode , but be sure to wear safety glasses.