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For this question it is important to note the a few concepts:
In the electric circuit depicted in the question there are two parts: the internal circuit and the external circuit. The internal circuit is the battery cells themselves. Work is done inside the cells, Mechanical Energy (ME), to generate (convert) the high Potential Energy (PE) at the positive terminal (positive side of the battery).
Energy moving along the wires in the circuit is referred to as current. In this particular question the lights, sounds, buzzers, etc. are connected in parallel known as a parallel circuit. In a parallel circuit the current flows through the various paths at the same time with more energy going to the path with the least resistance. This is much like a large river breaking down into a number of smaller streams where the stream with greatest capacity (or less obstacles) getting more water. Note: The total flow of water through the streams is equal to the total flow of the river feeding the streams. If one of the streams increases in capacity and/or reduces the obstacles (less resistance) there is a re-distribution of water amongst the other streams (assuming the larger river cannot pump down more water).
When connecting the internal circuit to the external circuit, and closing the switches, a natural flow of energy, current – see below, occurs much like a roller coaster car at the top of the hill. (I.e. Energy is required to move the car to the top of the track where the highest GPE is located. At the top the car makes a natural decline transforming the GPE to KE)
With the above notes we know that for each of A, B, C, and D the energy starts as Mechanical Energy inside the internal circuit. When any or all of the switches are closed, the current flows through the closed circuit. Note: In the answers, below, I will omit the fact that the first part is ME converting to PE in the internal circuit.
For A
PE to Electrical Energy (EE) to Light Energy (and Heat Energy)
For B
PE to EE to Light Energy (and Heat Energy) + Sound Energy
Note: The brightness of the bulb will decrease
For C
Note: It specifically states a Nichrome wire and has the wire coiled up. This has a double effect on resistance (heat energy). The coiling of the wire increases the length of the wire (increasing resistance) and increases the probability of the electrons colliding. This colliding causes heat. Nichrome as a material has a high resistance to current.
PE to EE to Heat Energy
Again we see the brightness of the bulb decreasing
The buzzer is not as loud
For D
Note: It appears as though the wire is the same as the wire carrying the current around the circuit (For this experiment we assume there is no resistance).
Closing the circuit at point D will allow the current to flow freely back to the negative terminals of the battery.
Since there is no resistance, and assuming the wire is able to accept the entire voltage of the combined batteries, the current will move almost entirely through this circuit.
There will be a significant decrease in the bulb's brightness (Light Energy) if any at all exists
There will be a significant decrease in the buzzer’s sound (Sound Energy) if any at all exists
There will be a significant decrease in the Heat Energy created from the Nichrome wire if any at all exists
The energy conversion through D would be PE -> EE -> ME (back in the internal circuit at the battery)
Also note, as can be seen very easily with a car battery, connecting the positive to the negative can cause sparks and explosions. Much of this will depend on the level of resistance on the wire (the material) and the design of the battery.
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