Question

In the circuit shown in the figure above, which switches must be closed in order for the light bulb to light up?

A. Only switches S1 and S2 need to be closed for the light bulb to light up.
B. Only switches S1 and S3 need to be closed for the light bulb to light up.
C. Only switch S1 needs to be closed for the light bulb to light up.
D. Only switches S2 and S3 need to be closed for the light bulb to light up.

Answer 1

the answer is b because from s1 it goes to s3 and then it can go through the center of s2 and s3 and resume its curcuit

Answer 2

Option B.

Explanation:

In a circuit shown in the figure two diodes are attached in which arrow shows the direction of current allowed by the diodes.

When key S1 is closed current flows from electric source to S1 then bulb. Afterwards if key S3 is closed current will pass through S3 and diode. Therefore to light the bulb circuit will be a closed circuit if S1 and S3 both are closed.

Therefore option B. is the correct answer.