6   9 The focal length and power of a converging glass lens are determined for the lens in air. The lens is then immersed in water. Which row in the table shows how the focal length and power of the lens change? A B C D Focal length Power of lens decreases decreases decreases increases increases decreases increases increases (Total for Question 9 = 1 mark) 10 A student used a Geiger-Müller (GM) tube to determine a value for the background count. He recorded the count for 2 minutes, every 15 minutes, as shown in the table. Time / min Count for 2 min 0 34 15 39 30 28 The counts are not the same. Which of the following is the reason for this? A The background count rate is random. B The counter is incorrectly calibrated. C The temperature has not stayed constant. D There is a systematic error in the measurement. (Total for Question 10 = 1 mark) Turn over 7   11 The lens of a mobile phone camera has a focal length of 4.25 mm. Light is focused onto light sensors at the back of the camera, as shown. lens light sensors (a) The camera is initially focused on an object in the far distance. Calculate the displacement of the lens that would be required to focus on an object 25.0 cm from the camera. (4) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. Displacement of lens = ...................................................... (b) State why the lens and the light sensors in a mobile phone camera can be positioned a fixed distance apart. (1) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (Total for Question 11 = 5 marks)