Assignment 3- Physics- Ideas and Implementation

Assignment 3 Zohair-Ul-Islam Ahmad

Assessment III

PART A

Demonstrating and Identifying properties of cathode rays using discharge tubes

- Containing a Maltase- Containing electric plates- With a fluorescent display screen- Containing a glass wheel

and analysing the information gathered to determine the sign of the charge on cathode rays

PART B

Summarise the effect of light on semiconductor in solar cells.

Student Name: Zohair-Ul-Islam Ahmad

Date: 9/05/2014

Class Year 12

Teacher Mr.Mohmmad Hasan

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Standard Discharge Tube


Aim:

Perform an investigation to demonstrate and identify properties of cathode rays using discharge tubes

Materials

• Induction Coil

• Transformers

•Magnet

•Plug to clip leads

•Discharge tubes containing:

- Crookes’ tube with a Maltese cross

- Cathode ray tube containing electric plates

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- Fluorescent display screen

- Glass wheel Discharge Tube

Method

1. Set up the induction coil (6V DC ). Switch off the power pack

2. Connect DC 6V to the induction coil primary

3. Connect the induction coil secondary to the electrodes of the discharge tube containing the Maltase cross (Crookes tube)

4. Ensure that the Maltase cross is vertical

5. Turn on the voltage supply

6. Adjust the induction coil to a high voltage output and observe the shadow of the cross at the end of the discharge tube

7. Repeat the observation with the cross lying horizontally

8. Replace the Crookes tube with the fluorescent screen display and record the effect of placing a set of bar magnets around the cathode ray

9. Use the Cathode ray tube containing electric plates

10.Use the paddle wheel by connecting it to the induction coil and observe the effect.

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Result 1) The Maltese cross is placed in the path of the cathode rays, causing a clearly defined

shadow at the end of the tube. It shows that cathode rays travel in straight lines and are blocked by solid objects.

2) With the cathode ray tubes containing the electric plates it shows that cathode

rays are associated with negative charges. The force produced by the plates electric fields cause the electrons to bend to the left or right depending on the polarity. When there is no force from the electric plates, the line is in the middle due to the fact that the forces of the electric and magnetic field are equal.

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3) The tube with the fluorescent screen, it shows that cathode rays can cause fluorescence. When the cathode rays collide with the air particles, the reaction produces light. This demonstrates that cathode rays have energy.

4) Using the cathode ray tube with the paddle wheel it shows that the lightweight glass paddle wheel is able to rotate freely and when it is placed in the path of the cathode rays so that the rays strike one edge of the wheel at a tangent. The cathode rays cause the wheel to spin and move away from the cathode. This demonstrates that

the cathode rays must have momentum, and therefore mass, and that they are emitted from the cathode.

Discussion

By conducting the experiment by the charged plates, we are able to conclude that cathode rays are negatively charged which means that they must have a negative signs – like electrons because they were attracted towards the positively charged plates and replelled by the negatively charged plate.

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The risk of this experiment which is dealt with is the production of X-Rays and the high input voltage necessary to operate the discharge tubes to avoid these risk the following precaution must be taken

- Remove all metal jewellery and watches.- Keep one hand behind your back to avoid forming a short circuit.- Do not handle the glass tubes while in use.- Use the equipment for a minimum amount of time.- Use the insulating handles on the connections.- Stand more than a metre from the apparatus.

The impact on society and the application of the properties of the Cathode Ray tube is based on the production of images by the CRO and Cathode Ray Tube television. Inside these devices contain an advance product of the standard Cathode Ray Tube,it consist of 3 parts

- Electron Gun - Deflecting Plates- Fluorescent Screen

The function of the following parts are that the electron gun get s an source of energy which heats up the filament in cathode resulting to the release of electrons by thermionic emissions. The 2 electrodes focus the beam at a single point which the anode develops a strong magnetic field exerting a force on electrons. The horizontal and vertical plates allow the beam to move up, down, left and right . The fluorescent screen is coated with a material that when struck by electrons, it emit light hence the production of an image.

Conclusion

•It was concluded in the experiment that cathode rays:

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- are electrons (from the electric plates )- travel in a straight line and do not go through solid objects( proven from the Maltase

Cross)- are negatively charged ( demonstrated by the electric plates)- collide with air to produce a fluorescent light (verified by the fluorescent tube)- have momentum and mass. (shown by the paddle wheel)

Part B

Summarise the effect of light on semiconductors in solar cells

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Solar cells are photovoltaic devices composed of semiconductor material such as silicon. Usually a p-n junction is used. This is a junction formed between a piece of n-type silicon and a piece of p-type silicon. An electric field is set up at the junction and this forms a potential barrier that forces any free electrons in the silicon to move to the n-type silicon and any holes to move to the p-type silicon. Light shining on the semiconductor material frees electrons (photoelectric effect) from the valence band to the conduction band of the semiconductor material, thus producing electron-hole pairs in the semiconductor. A photon of light with energy greater than the band gap energy between the valence and conduction bands but less than the work function energy for the semiconductor strikes an electron and is absorbed. This gives the electron sufficient energy to jump the forbidden energy gap from the valence to the conduction band.

Once the electron is free it is forced by the barrier potential to move to the n-type material, while the hole left behind is forced to move to the p-type material. If an external circuit is supplied, the electron will move out of the n-type material, around the external circuit through a load and back into the p-type material to recombine with the hole. Clearly, as many electrons undergo the same process, an electric current has been produced by the solar cell. The size of the current produced is proportional to the light intensity incident on the solar cell. Overall, light energy has been transformed into electrical energy.

Reference

Google.com.sa

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Google Images

In-text: (Google.com.sa, 2014)

Bibliography: Google.com.sa, (2014). Google Images. [online] Available at: https://www.google.com.sa/imghp?hl=en&tab=wi [Accessed 7 May. 2014].

BookPhysics 2 HSC course

McCallum, Y. and Andriessen, M.

Physics 2 HSC course

In-text: (McCallum and Andriessen, 2008)

Bibliography: McCallum, Y. and Andriessen, M. (2008). Physics 2 HSC course. 1st ed. Milton, Qld.: John Wiley & Sons.

Website

Miac.unibas.ch

In-text: (Miac.unibas.ch, 2014)

Bibliography: Miac.unibas.ch, (2014). [online] Available at: http://miac.unibas.ch/PMI/01-BasicsOfXray-media/figs/crookes_maltese_cross_tube.jpg [Accessed 7 May. 2014].

WebsiteInvestigating Cathode Rays

Schools.cbe.ab.ca

Investigating Cathode Rays

In-text: (Schools.cbe.ab.ca, 2014)

Bibliography: Schools.cbe.ab.ca, (2014). Investigating Cathode Rays. [online] Available at: http://schools.cbe.ab.ca/b858/dept/sci/teacher/zubot/phys30notes/investnurays/investnurays.htm [Accessed 28 Apr. 2014].

Website

University, C.

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HSC Online - From ideas to implementation: 1. Cathode rays

In-text: (University, 2014)

Bibliography: University, C. (2014). HSC Online - From ideas to implementation: 1. Cathode rays. [online] Hsc.csu.edu.au. Available at: http://www.hsc.csu.edu.au/physics/core/implementation/9_4_1/941net.html [Accessed 27 Apr. 2014].

WebsitePhysics Explorer

Web3.karabar-h.schools.nsw.edu.au

Physics Explorer

In-text: (Web3.karabar-h.schools.nsw.edu.au, 2014)

Bibliography: Web3.karabar-h.schools.nsw.edu.au, (2014). Physics Explorer. [online] Available at: http://web3.karabar-h.schools.nsw.edu.au/moodle/cds/physics/index.htm [Accessed 13 Apr. 2014].

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Assignment 3- Physics- Ideas and Implementation