Physics questions help (1 Viewer)

[Real Madrid]

I need answers for the past HSC questions listed below

Question 21 (5 marks)

(a) Explain the relationship between the current in the primary coil and the current in the secondary coil of an ideal step-down transformer in relation to the conservation of energy. (3 marks)

(b) Explain why a transformer will work in AC circuit but not in DC circuit. (2 marks)

Question 26 (6 marks)

An electricity substation delivers a current of 10A at a voltage of 6kV to an office complex. The office complex uses a transformer to provide a current of 230 A at a voltage of 240 V.

(a) Explain why AC is preferable to DC as an input current for transformers. (2 marks)

(b) Outline possible causes of energy loss in the transformer. (2 marks)

(c) Calculate the energy loss by the transformer in eight hours. (2 marks)

 

[MrLuvable]

Question 21 (5 marks)

(a) Explain the relationship between the current in the primary coil and the current in the secondary coil of an ideal step-down transformer in relation to the conservation of energy. (3 marks)

The Principal of Conservation of Energy states that energy cannot be created nor destroyed but that it can be transformed from one form to another. This means that if a step-up transformer gives a greater voltage at the output, there must be some kind of trade-off. The rate of supply of energy to the primary coil must be greater that or equal to the rate of supply of energy from the secondary coil. For example, if 10 A is suuplied each second to the primary coil, then the maximum amount of energy that can be obtained each second from the secondary coil is 10A.

P.s. Not a 100% sure about this one.

(b) Explain why a transformer will work in AC circuit but not in DC circuit. (2 marks)

Trasnformers only work on AC because they require a changing current to create a changing magnetic flux in the core. Thus, the constant supply of DC would not produce a changing magnetic flux so no voltage will be induced in the secondary coil.

 

[MrLuvable]

An electricity substation delivers a current of 10A at a voltage of 6kV to an office complex. The office complex uses a transformer to provide a current of 230 A at a voltage of 240 V.

(a) Explain why AC is preferable to DC as an input current for transformers. (2 marks)

AC is more preferable over DC as it provides a changing current which as a result creates a changing magnetic flux in the core. If the input current was DC, it would not produce a changing magnetic flux thus no voltage would be induced in the secondary coil.

(b) Outline possible causes of energy loss in the transformer. (2 marks)

Transformers have no moving parts thus are very efficient devices. Efficiency approximately = 95%. Modern transformers convert more thant 95% of electrical input energy to electrical output. Though some losses of energy does occur. These losses can be accredited to Eddy Currents. Transformers cores are laminated to minimise Eddy currents.

(c) Calculate the energy loss by the transformer in eight hours. (2 marks)

 

[helper]

Question 21 (5 marks)

(a) Explain the relationship between the current in the primary coil and the current in the secondary coil of an ideal step-down transformer in relation to the conservation of energy. (3 marks)

The Principal of Conservation of Energy states that energy cannot be created nor destroyed but that it can be transformed from one form to another. This means that if a step-up transformer gives a greater voltage at the output, there must be some kind of trade-off. The rate of supply of energy to the primary coil must be greater that or equal to the rate of supply of energy from the secondary coil. For example, if 10 A is suuplied each second to the primary coil, then the maximum amount of energy that can be obtained each second from the secondary coil is 10A.

Amperes are not the unit of energy. The basis of your answer is correct till you reached there.





Since the secondary coil has less coils it has less magnetic flux, so the change in flux will be less and the induced EMF will be smaller. Since Energy must be conserved, if is smaller, then secondary current must be larger.

(b) Explain why a transformer will work in AC circuit but not in DC circuit. (2 marks)

Trasnformers only work on AC because they require a changing current to create a changing magnetic flux in the core. Thus, the constant supply of DC would not produce a changing magnetic flux so no voltage will be induced in the secondary coil.

Transformers will work on DC but only if the current is constantly turned on and off like in an induction coil or with a non-smoothed DC, where the current is constantly increasing and decreasing but the current remains in the same direction