Diffraction and lensesIB MYP Sciences: Flashcards

Exam questions on Diffraction and lenses

1. Waves in a harbour at Mombasa pass through a narrow gap in a sea wall into a sheltered bay. The gap is about 5 m wide, which is similar to the wavelength of the waves.
   Describe the shape of the waves after they pass through the 5 m gap and state what happens to their wavelength.2 marks
2. A student uses a converging lens as a magnifying glass to read the small print on a medicine label. The lens has a focal length of 10 cm.
   Describe the image that the student sees when the label is in the correct position.2 marks
3. A group of students tests the idea that the more curved a converging lens is, the shorter its focal length. They use two lenses made of the same glass and with the same diameter: lens A is strongly curved and lens B is gently curved. Each lens is used to focus the image of a distant window onto a white screen, and the distance from the lens to the screen is measured with a metre rule. Four readings are taken for each lens. For lens A the readings are 9.8 cm, 10.2 cm, 10.0 cm and 10.0 cm. For lens B they are 19.6 cm, 20.4 cm, 20.0 cm and 20.0 cm.
   Calculate the mean focal length of each lens and state whether the results support the students' idea.3 marks