P1 – Foundations – part 1 Sound and Light

Convex lens Focal point – where the rays meet. Focal length – Distance from lens to focal point. (real images are formed at 2 times the focal length) Real image – formed by the focused rays. Real images are usually upside down and magnified (though rarely the same size as the original) and captured on a screen. Virtual image - Image appears not where the rays are focused, like a mirror. ( can be in front of the lens or at half the focal length)

AnswerAcceptable answersMark (a)(i) C on a screen (1) (a)(ii) Explanation linking the following:- (measure) distance / length / from / line (1) lens to image / screen / focal point (1) how far away use ruler / tape measure measure u(object distance) and v(image distance) calculate focal length using 1/u + 1/v = 1/f (measure) from lens to image (2) (2)

(a)(i)A the focal length (1) (1) (a)(ii) smaller than (1) real (1) (2) (b)  Any (more or less) straight ray which changes direction inside the lens (1) Ray does not need to touch far side. Allow slight discontinuities Ignore any ray drawn beyond the 2 nd surface and any reflected ray(s). Ignore any extra incident rays. (1)

Types of telescopes Refracting Can be smaller and easier to use/hold. Uses refraction (bending light) to create a real image. Magnifies distant object.

Reflecting Brighter image Clearer image Magnified real image Uses mirrors apart from eye piece which is a lens.

Exam question *(b) Describe the similarities and differences between refracting telescopes and reflecting telescopes. (6)

A description including some of the following Similarities both use lenses (lenses) acts as eyepieces both produce images of distant objects eyepiece magnifies (eyepiece magnifies) real image produced by objective in both Differences reflector uses mirror (reflector uses mirror ) as objective / to collect light refractor uses lens (refractor uses lens) as objective / to collect light reflector can collect more light than a refractor reflector reduces abberation /gives better quality image / ORA refractors are easier to support / ORA

For all 6 marks A detailed description to include both similarities and differences with a clear description of the comparison e.g. the eyepiece in each produces a magnified image of the objective image. The reflector has a mirror as the objective while the refractor has a lens the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors

Infra sound and Ultra sound Human hearing is 20 – 20,000 Hertz. Below human hearing is Infrasound. Above human hearing is ultra sound. Infrasound is used by animals to communicate (whales, elephants), to detect volcanic eruptions or meteors. Ultrasound is used to create images by timing how long it takes to reflect off an object and return to the sensor. (sonar, baby scans, detect damage/cracks in metal pipes).

A man uses a dog whistle to call his dog. The whistle uses ultrasound. (i) The dog can hear the whistle but the man cannot. Explain why the dog can hear the whistle but the man cannot hear the whistle. (2) (ii) The dog is 140 m away from the man. The ultrasound takes 0.42 s to travel from the man to the dog. Calculate the speed of ultrasound. State the unit. (3) speed of ultrasound = unit =

(b) (i) An earthquake P-wave has a frequency of 15 Hz. Complete the sentence by putting a cross ( ) in the box next to your answer. The earthquake P-wave is (1) A an infrasound wave B an ultrasound wave C an electromagnetic wave D a transverse wave