Question
3a. Briefly write on the following methods of producing polarized light i. Reflection ii. Double Refraction iii. Diffraction iv. Absorption 3b. Distinguish between the following: 1. Plane and cross polarized light ii. Analyser and polarizer 4a. Briefly outline four(4) differences between isotropic and anisotropic minerals 4b. State six(6) precautions observed in the use of the petrographic microscope 5a. State four optical properties of minerals that can be studied under PPL and XPL 5b. Explain the following optical properties of minerals. ii. relief iii. Birefringence 6. Write short note on the following b. interference figure of uniaxial mineral Smks each a. extinction d. Refractive index c. twinning 16mks 4mks 8mks 12mks 12mks
Answer
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Matilda
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Answer
### 3a. Methods of producing polarized light:i. Reflectionii. Double Refractioniii. Diffractioniv. Absorption3b. Distinguish between:1. Plane and cross polarized lightii. Analyser and polarizer4a. Differences between isotropic and anisotropic minerals:1. Optical Properties2. Refractive Index3. Behavior Under Polarized Light4. Crystal Symmetry4b. Precautions in using the petrographic microscope:1. Ensure cleanliness2. Appropriate lighting3. Handle slides carefully4. Calibrate regularly5. Avoid excessive force6. Proper storage5a. Optical properties of minerals under PPL and XPL:1. Pleochroism2. Relief3. Birefringence5b. Explanation of optical properties:i. Pleochroismii. Reliefiii. Birefringence6. Short notes:b. Interference figure of uniaxial minerala. Extinctiond. Refractive indexc. Twinning
Explanation
## Step1: Methods of Producing Polarized Light### 1. **Reflection**: When light reflects off a non-metallic surface at a specific angle (Brewster's angle), the reflected light becomes polarized parallel to the surface.2. **Double Refraction**: Certain crystals, like calcite, split an incoming light beam into two rays with perpendicular polarization states.3. **Diffraction**: Polarization can occur when light passes through a diffraction grating, causing interference patterns that can polarize light.4. **Absorption**: Materials like Polaroid filters absorb one component of the light's electric field, allowing only the perpendicular component to pass through, thus polarizing the light.## Step2: Distinguishing Between Concepts### 1. **Plane and Cross Polarized Light**: Plane polarized light oscillates in a single plane, while cross polarized light involves two perpendicular polarizing filters, blocking all light unless the sample between them rotates the plane of polarization.2. **Analyser and Polarizer**: A polarizer is a device that produces plane polarized light from unpolarized light, while an analyser is used to detect the plane of polarization of light, often used in conjunction with a polarizer.## Step3: Differences Between Isotropic and Anisotropic Minerals### 1. **Optical Properties**: Isotropic minerals have the same optical properties in all directions, while anisotropic minerals have different optical properties depending on the direction.2. **Refractive Index**: Isotropic minerals have a single refractive index, whereas anisotropic minerals have multiple refractive indices.3. **Behavior Under Polarized Light**: Isotropic minerals remain dark under crossed polarizers, while anisotropic minerals show interference colors.4. **Crystal Symmetry**: Isotropic minerals are typically cubic, while anisotropic minerals can belong to any other crystal system.## Step4: Precautions in Using the Petrographic Microscope### 1. Ensure the microscope is clean and free of dust.2. Use appropriate lighting to avoid overheating the sample.3. Handle slides carefully to avoid scratches.4. Calibrate the microscope regularly for accurate observations.5. Avoid using excessive force when adjusting the focus.6. Store the microscope in a dry, dust-free environment.## Step5: Optical Properties of Minerals Under PPL and XPL### 1. **Pleochroism**: Variation in color of a mineral when observed from different angles under plane polarized light.2. **Relief**: The apparent height of a mineral grain relative to the mounting medium, observed under plane polarized light.3. **Birefringence**: The difference in refractive indices in different crystallographic directions, observed under crossed polarized light.## Step6: Short Notes on Optical Properties### 1. **Interference Figure of Uniaxial Mineral**: A pattern observed under crossed polarizers when viewing a uniaxial mineral, showing concentric rings and isogyres indicating optical properties.2. **Extinction**: The phenomenon where a mineral goes dark under crossed polarizers at specific orientations due to alignment of its optical axis with the polarizer.3. **Refractive Index**: A measure of how much light is bent, or refracted, when entering a mineral.4. **Twinning**: The intergrowth of two or more crystal segments of the same mineral in a symmetrical manner.