Explain what is “wave constructive interference” in regard to amplitude.
I need it by tmr by midnight Please help.

Aresistor with an unknown resistance is connected in parallel to a 9 ω resistor. when both resistors are connected in parallel to an emf source of 21 v, the current through the unknown resistor is measured with an ammeter to be 4 a. what is the resistance of the unknown resistor? answer in units of ω.

Consider a file currently consisting of 200 blocks. assume that the file control block (and the index block in the case of indexed allocation) is already in memory. calculate how many disk i/o operations are required for contiguous, linked, and indexed (single-level) allocation strategies, for each of the conditions listed below. in the contiguous-allocation case, assume that there is not room to grow at the beginning but there is room to grow at the end. also assume that the block information to be added is stored in memory.

Astudent pushes a 40-n block across the floor for a distance of 10 m. how much work was applied to move the block? a. 4 j b. 40 j c. 400 j d. 4000 j