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It is an appliance used to compare the illuminating powers (luminous intensity) of two sources of light. The following types of photometers are in common use: (1) Rumford photometer (2) Bunsen’s grease-spot photometer (3) Bouguer’s photometer (4) Joly’s photometer (5) Lummer-Brodhum photometer (6) Flicker photometer (7) Photo-voltaic photometer. Lummer and Brothum photometer S1 and S2 are two sources of illuminating powers L1 and L2 respectively. These two lamps S1 and S2 are placed on the opposite side of a white opaque screen and the diffused reflected light from the two faces of the screen is incident on the two identical prisms P1 and P2. The light after reflection from these prisms passes through the Lummer-Brothum cube AB. The Lummer-Brothum cube consists of two right angled isosceles prisms A and B in contact with each other. The edges of the prism A are cut in such a way that a film of air exists between the two surfaces of contact. It will be seen that light rays are totally internally reflected at all the points in the two prisms except at the centre. Thus in the field of view of the telescope it is observed that either (i) the inner portion is dark as compared to the outer or (ii) the outer portion is dark as compared to the inner portion. For balancing the distance of one source is fixed and the distance of the other adjusted that the field of view is equal bright. When the field of view is equally bright the balance is said to have been obtained. Theory: After the photometric balance has been obtained let the distance of the source S1 from the screen be R1 and the distance of the source S2 from the screen be R2. Here θ = 0 ∴ cos θ = 1 If r1 is the reflecting power of the surface F1 and r2 is the reflecting power of the surface F1, then If r1 = r2 i.e. the two faces of the screen have the same reflecting power Note: This photometer cannot be used when the two sources emit light radiations wavelengths (colours). Services: - Photometer Homework | Photometer Homework Help | Photometer Homework Help Services | Live Photometer Homework Help | Photometer Homework Tutors | Online Photometer Homework Help | Photometer Tutors | Online Photometer Tutors | Photometer Homework Services | Photometer
It is an appliance used to compare the illuminating powers (luminous intensity) of two sources of light. The following types of photometers are in common use: (1) Rumford photometer (2) Bunsen’s grease-spot photometer (3) Bouguer’s photometer (4) Joly’s photometer (5) Lummer-Brodhum photometer (6) Flicker photometer (7) Photo-voltaic photometer. Lummer and Brothum photometer S1 and S2 are two sources of illuminating powers L1 and L2 respectively. These two lamps S1 and S2 are placed on the opposite side of a white opaque screen and the diffused reflected light from the two faces of the screen is incident on the two identical prisms P1 and P2. The light after reflection from these prisms passes through the Lummer-Brothum cube AB. The Lummer-Brothum cube consists of two right angled isosceles prisms A and B in contact with each other. The edges of the prism A are cut in such a way that a film of air exists between the two surfaces of contact. It will be seen that light rays are totally internally reflected at all the points in the two prisms except at the centre. Thus in the field of view of the telescope it is observed that either (i) the inner portion is dark as compared to the outer or (ii) the outer portion is dark as compared to the inner portion. For balancing the distance of one source is fixed and the distance of the other adjusted that the field of view is equal bright. When the field of view is equally bright the balance is said to have been obtained. Theory: After the photometric balance has been obtained let the distance of the source S1 from the screen be R1 and the distance of the source S2 from the screen be R2. Here θ = 0 ∴ cos θ = 1 If r1 is the reflecting power of the surface F1 and r2 is the reflecting power of the surface F1, then If r1 = r2 i.e. the two faces of the screen have the same reflecting power Note: This photometer cannot be used when the two sources emit light radiations wavelengths (colours).
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