OCR 2023 Design and Technology H404/01: Principles of Design Engineering A Level Question Paper & Mark Scheme (Merged)

This shows a USB-powered personal mini fan. fan blade flexible stem (a) The flexible stem of the personal mini fan is covered with PVC. PVC is a thermo softening polymer. Identify two reasons why a thermo softening polymer is a suitable material for the flexible stem. 1 ................................................................................................................................................ ................................................................................................................................................... 2 ................................................................................................................................................ ................................................................................................................................................... [2] (b) Explain why bearings are needed in mechanical systems such as those used in the personal mini fan. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...........................................................................................................................................[2] DC motor USB 3 © OCR 2023 Turn over (c) The personal mini fan is powered by plugging it in to a USB socket. Explain one benefit to the user and one benefit to the manufacturer of designing the personal mini fan to be powered from a USB socket. Benefit to user .......................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Benefit to manufacturer ............................................................................................................ ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [4] 4 © OCR 2023 Power dissipated in variable resistor VR1 ................................ W (d) The personal mini fan contains a DC motor. A designer wishes to develop a personal mini fan product by adding a control to adjust the speed of the motor. Different circuits are being considered to achieve this. This circuit shows how a variable resistor VR1 is used to control the speed of the motor. + (i) When variable resistor VR1 is set at 20Ω, the fan runs at 1 its maximum speed. At this speed, the current flowing through the circuit is 250mA. 2 Calculate the power dissipated in variable resistor VR1 when it is set at 20Ω. Give your answer in W and show your working.