The diagram shows a kitchen toaster being examined after it stopped heating. The toaster is rated at 1.8 kW and uses a 230 V supply. Its heating element is ...
Question 1 Report
The diagram shows a kitchen toaster being examined after it stopped heating. The toaster is rated at 1.8 kW and uses a 230 V supply. Its heating element is a coil of high-resistance wire. When current passes through the coil, the element becomes hot enough to toast bread. A technician finds that the coil is broken at one point. The toaster also has a plastic outer case and a metal crumb tray.
(a) Explain why the heating element is made from a material with high resistance. [2]
(b) Calculate the current in the toaster when it is operating normally. [2]
(c) Give one reason for using a plastic outer case. [1]
A smoke alarm in a rented house is powered by a 9 V battery. Fig. 1 shows the battery connected to a buzzer and a switch operated by smoke particles. When the switch closes, current flows through the buzzer and sound waves warn the residents. During a monthly check, the alarm makes only a faint sound. The landlord replaces the battery rather than bypassing the warning device.
(a) Name the component that provides the potential difference in this circuit. [1]
(b) Describe the energy changes in the buzzer when the alarm operates. [2]
(c) Explain why a weak battery can make the sound quieter. [1]
Answer Details
Toaster
(a) A high-resistance heating element transfers electrical energy to thermal energy effectively when current flows. This gives a large heating effect, making the coil hot enough to toast bread. [2]
(b) \[I=\frac{P}{V}=\frac{1800\text{ W}}{230\text{ V}}=7.83\text{ A}\approx7.8\text{ A}\]
[2]
(c) Plastic is an electrical insulator, reducing the risk of electric shock. [1]
Smoke alarm
(a) The component that provides potential difference is the battery, or cell. [1]
(b) Chemical energy in the battery is transferred to electrical energy. In the buzzer, electrical energy is transferred mainly to sound energy, with some thermal energy. [2]
(c) A weak battery provides a lower potential difference, giving a smaller current and less power transferred to the buzzer. The sound is therefore quieter. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
