# [SPM Physics Quantum Question] How to solve question (b)(i)? The answer is 3.06×10^-19 J

### Question

13.6. Rajah 13.6 menunjukkan sebatang penunjuk laser menghasilkan pancaran yang mempunyai kuasa 1.5mW dan panjang gelombang 6.5 \times 10^{-13} m.
Diagram 13.6 shows a laser pointer produces a beam of power 1.5mW and wavelength of 6.5 \times 10^{-13} m

a) Zarah-zarah pancaran laser dikenali sebagai foton.
The particle of laser beam known as photon.
(i) Apakah maksud foton?
What is meant by photon?
[1 markah]

(ii) Berikan satu ciri foton.
Give one characterisitc of photon.
[1 markah]

(b) Diberi h=6.33 \times 10^{-34} Js, c= 3 \times 10^8 ms^{-1} , hitung
Given h=6.33 \times 10^{-34} Js, c= 3 \times 10^8 ms^{-1}, calculate
(i) tenaga foton
the energy of a photon.
[2 markah]

### Answer

Hi Farhaini,
I believe that your working is entirely correct and it’s the question that gave the incorrect information.

To get the mark scheme answer,
Planck’s constant should be 6.63 \times 10^{-34} Js and wavelength given should be 6.5 \times 10^{-7} m instead of 6.5 \times 10^{-13} m ! An EM wave with a wavelength of magnitude 10^{-12} m or smaller is already in the gamma ray spectrum, a gamma-ray laser hasn’t been invented up to this day hahaha when we talk about laser beam it’s usually in the visible light spectrum or infrared spectrum.

Hope this helps!

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Wahhh you are so smart any tips so that I can be smart too?

I’m not smart haha, I just finished A levels and still remember some stuff from this topic actually but from the way you ask questions and from your working I can tell that you’re a smart student too! Practicing more state papers and making sure you understand the questions and concepts is a great way to prepare for SPM (even though some of them have a lot of errors haha ) All the best Farhaini! I believe that you will do well for your SPM! ^w^

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Wahh Thank you very muchh!! I will try my best

1 Like