Given: A and B are input terminals. Logic 1 => 5V, Logic 0 => <1V. Which logic gate operation does the following circuit perform?

Since, when A and B both are logic 1 then no current will flow through the both 50Ω resistors, because both the diodes will not conduct. Therefore, the whole current will flow through R=10K and the output is the potential difference across the R=10K which will be 6V in this case, meaning high. Now, when either of the inputs is low, current through the terminal which is low will flow through it and most of the current will flow through the 50Ω resistance since it is very very less than R=10K. Therefore, the potential across R=10K will be less than 1V. Hence, when either of the inputs is low, the output is also low. When both the inputs are low, the same case as when either of the inputs is low will be there, hence the output will also be low. Therefore, the above circuit acts as an AND Logic gate.