This charger is used at a community library to charge tablet computers from the mains supply. Fig. 1 shows the plug, transformer and charging cable. The tra...
Question 1 Report
This charger is used at a community library to charge tablet computers from the mains supply. Fig. 1 shows the plug, transformer and charging cable. The transformer reduces the 230 V alternating potential difference from the mains to 5.0 V for the tablet. A student says that the transformer creates electrical energy. The technician explains that it transfers energy between circuits and some energy is dissipated as thermal energy. The tablet charger provides a current of 2.0 A for 45 minutes.
(a) What type of transformer is shown in Fig. 1? [1]
(b) Describe the energy transfer in the transformer. [2]
(c) Calculate the charge transferred to the tablet in 45 minutes. [3]
(d) Calculate the electrical energy supplied to the tablet during this time. [3]
(e) Give one reason why a transformer is needed before the cable reaches the tablet. [1]
Answer Details
(a) This is a step-down transformer, because it reduces the potential difference from 230 V to 5.0 V. [1]
(b) Electrical energy is transferred from the primary circuit to the secondary circuit. Some energy is dissipated as thermal energy, and possibly sound, so the transformer does not create energy. [2]
(c)
\[45\text{ minutes}=45\times60=2700\text{ s}\]
\[Q=It=2.0\text{ A}\times2700\text{ s}=5400\text{ C}\]
The charge transferred is 5400 C. [3]
(d) Use \(E=VQ\):
\[E=5.0\text{ V}\times5400\text{ C}=27000\text{ J}\]
The electrical energy supplied is 27 000 J. [3]
(e) The 230 V mains supply could damage the tablet. The transformer provides the much safer 5.0 V needed by its electronics. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
