Transformer and electric energy – problems and solutions

1. The primary coil of an ideal transformer connected to a voltage source and the secondary coil is connected to the lamp as shown below.

Transformer and electric energy – problems and solutions 1A. The lamp will dim if the primary loops are reduced

B. The lamp will be brighter if the secondary loops are increased

C. The lamp will be dimmer if the primary voltage is increased

D. The lamp will be lighter if the primary loops are reduced

E. The light will be the same if loops are changed

Solution

The change in the number of coil loops affects only the type of transformer. If the primary loops reduced so that the secondary loops are more then this transformer becomes a step-up transformer that raises the voltage. Likewise, when the coil loops are coupled so that the secondary coil loops is less then this transformer becomes a step-down transformer that lowers the voltage.

Keep in mind that when the power voltage increases, the electric current strength decreases so that the electric power is constant (P = V I). Electrical power is the change of electrical energy over a certain time interval. When the input power is equal to the output power the amount of energy consumed is also the same.


Light or dim light is associated with many or at least electrical energy that is converted into light energy. If a lot of electrical energy is converted into light energy then a bright light, otherwise if a little electrical energy is converted into light energy then the light is dim. The electric power is constant, the electric energy is also constant so the light is the same.

The correct answer is E.

2. The image below describes the ideal transformer. The primary coil is connected to a voltage source and the secondary coil is connected to a lamp (L). Then the condition of the lamp will be…

Transformer and electric energy – problems and solutions 2A. Normal brightness when the primary loops are changed

B. Dimmed when primary voltage increased

C. Bright when secondary loops are increased

D. Dimmed when secondary loops are increased

E. Brighter when the primary loops are reduced

Solution :

Input power = P = V I = (200 Volt)(2 Ampere) = 400 Watt = Output power

The transformer only reduces the voltage but does not reduce the electrical power. Electric power kept constant therefore when the electric voltage decreases, the electric current increases (P = V I). The input electrical power the same as the output power so that the electrical energy used during a certain time interval is also the same. Thus light is normal or unchanged.

The correct answer is A.

3.

The secondary coil is connected to a bulb lamp, while the primary coil is connected to a voltage source. The light bulb will turn on …

A. brighter if the number of primary loops is increasedTransformer and electric energy – problems and solutions 3

B. brighter if the number of secondary loops is increased

C. brighter if the number of secondary loops is equal to the primary

D. dimmed when the primary voltage is increased

E. dimmed when the primary voltage and the number of secondary loops are increased

Solution

There is no correct answer