Instrumentation of UV-Visible Spectroscopy and MCQ With Answer

  1. RADIATION SOURCE :-  it is required ideal condition that are given below :-
  •  It should be stable and not allow fluctuations.
  •  It should be continuing emitting light.
  • It should be not show fatigue on continuing use.
  • It should provide incident light of sufficient intensity for the transmitted energy to be detected at the end of optical path.

There are following type of radiation source are used in UV-VISIBLE SPECTROSCOPY

1. Tungsten Halogen lamp:-

It is construction is similar to house hold lamp.  The bulb contain a filament and it is filled with inert gas like He, Ar etc.

Filament heated at 3000k temperature after 3000k temp. It is started to generate radiation.

It is used when polychromatic light are required.

2. Hydrogen Discharge lamp :-

In Hydrogen Discharge lamp are pair of electrodes that are enclosed in glass tube.

This glass tube is filled with H2 gas.

When current is passed through these electrod at high voltage, discharge of electron

This electron are responsible for the excited hydrogen molecules which in turn cause emissions of U.V.

3. Xenon Discharge Lamp :-

It possessed two tungsten electrod separated by some distance.

These are enclosed in a glass tube and xenon gas is filled under pressure.

An intense arc is formed between electrod by applying high voltage.

This is a good source of continuous plus additional intense radiation.

It intensity is higher than the Hydrogen discharge lamp.

4. Mercury arc lamp :-

In Mercury arc lamp , Mercury vapour is stored under high pressure and excitation of Mercury atom is done by electric discharge.

Collimating system :-

The radiation emitted by the radiation source is collimated by lense, mirror and slits.


Materials used for the lenses must be transparent to the radiation being used.

Ordinary silicate glass transmit between 350 to 300 nm and is suitable for visible and near IR region.

Quartz or fused silica is used as a material for lenses to work below 300 nm.


These are used to reflect  focus or collimate light beam in spectrophotometer.

Slits :- 

Slits is an important device in resolving polychromatic radiation into monochromatic radiation. To achieve this entrance slit and exit slit are used.

Monochromator :-

It is  device used to isolate the radiation of the desired wavelength from wavelength of the continuous spectra.

MONOCHROMATOR has following unit

1. Entrance slit ( to get narrow source)

2. Dispersing slit (disperses the heterochromatic radiation into it components )

3. Exit slit ( Allow the nominal wavelength together with a bond of wavelength on either side of it)


1. Prisms :- The prism disperse the light radiation into individual colour or wavelength.

The band pass is lower than that of filter and hence it has better resolution.

2. Grating :- Grating are the most efficient one in converting a polychromatic to monochromatic light.

It is used to achieve 0.1 nm resolution.

Grating are of two types

1. Diffraction grating :-

Grating are nothing but ruling made on some material like glass , quartz, or alkyl halide depending upon the instrument whether it is visible / IR/UV spectrophotometer

2. Transmission grating :-

Transmission grating is similar to diffraction grating, but refraction take place instead of reflection.


1. Tungsten lamp filament has required how much temperature ?

A. 2000k

B. 3000k

C. 4000k

D. 5000k

2.How much range wavelength is transmit by silicate glass ?

A. 100 nm to 200 nm

B. 200nm to 300 nm

C. 300 nm to 350 nm

D. 10nm to 40 nm

3. what is role of slit in uv-visible spectroscopy ?

A. Monochromatic radiation to polychromatic radiation.

B. Polychromatic radiation to monochromatic radiation.

C. A and B

D. None of this

4. Which radiation source has electrode in its construction ?

A. Tungsten lamp

B. Hydrogen discharge lamp

C. Xenon Discharge Lamp

D. Mercury lamp

5. Which device is used to isolate the radiation of the desired wavelength from wavelength of the continuous spectra ?

A. Monochromator

B. Radiation source

C. Recorder

D. None of this

6. Diffraction grating is consists of a

A. Glass

B. Quartz

C. Alkyl halide

D. All of the above

7.  The work of Entrance slit is?

A. To get narrow source

B. To render light parallel

C. To disperse radiation

D. To fall on sample cell

8. Collimator  is used for?

A. To reform the image of the entrance slit.

B. To get narrow source

C. To fall on sample cell

D. To disperse radiation

9. Exit slit used for

A. To reform the image of the entrance slit.

B. To get narrow source

C. To fall on sample cell

D. To disperse radiation

10. Which type of vapour is stored in Mercury lamp ?

A. Mercury vapour

B. Hydrogen vapour

C. Xe

D. Ozone

Answer key

1. B

2. C

3. B

4. B

5. A

6. D

7. A

8. A

9. C

10. A

Reference take the book of pharmaceutical analysis thrid edition of the ravi sankar





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