Sunday, December 11, 2011
Saturday, December 3, 2011
Saturday, November 19, 2011
Concave mirror applications
used by dentist to see magnified image of the teeth
an eye specialist using ophthalmoscope
Friday, November 18, 2011
LIGHT
CLASS-VII
WORKSHEET
Q1. The focal length of a spherical mirror is 10cm. What is the radius of curvature of this spherical mirror?
Q2. Name a mirror that gives an erect and magnified (enlarged) image of an object.
Q3. Where should an object be placed on the principal axis of a concave mirror so that its real image is of the same size as that of the object?
Q4. Name the rear-view mirror used in vehicles.
Q5. No matter how far you stand from a mirror, your image appears erect. The mirror is:
i) plane
ii) convex
iii) concave
iv) either plane or convex
Q6. Name the type of mirror which always forms a virtual and diminished image.
Q7. A man standing in front of a magical mirror, finds his image having a very small head, a fat body and legs of normal (same) size. What type of mirrors are used in this magical mirror?
Q8. Differentiate between virtual image of a concave mirror and of a convex mirror.
Q9. The angle between the incident ray and the mirror is 40.
i) What is the angle of incidence?
ii) What is the angle of reflection?
Q10. Explain lateral inversion.
Q11. How can you distinguish between a plane mirror, a concave mirror and a convex mirror without touching them?
Q12. The minimum distance between an object and its real image formed by a concave mirror is _________.
Friday, July 15, 2011
What is a Thermometer?
Thermometers measure temperature, by using materials that change in some way when they are heated or cooled. In a mercury or alcohol thermometer the liquid expands as it is heated and contracts when it is cooled, so the length of the liquid column is longer or shorter depending on the temperature.Daniel Gabriel Fahrenheit was the German physicist who invented a alcohol thermometer in 1709, and the mercury thermometer in 1714. In 1724, he introduced the standard temperature scale that bears his name - Fahrenheit Scale - that was used to record changes in temperature in an accurate fashion.
In 1742, the Celsius scale was invented by Swedish Astronomer Anders Celsius. The Celsius scale has 100 degrees between the freezing point (0°C) and boiling point (100°C) of pure water at sea level air pressure.
The liquid used in laboratory thermometer can be pure ethanol or toluene or kerosene, depending on manufacturer and working temperature range. Since these are transparent, the liquid is made more visible by the addition of a red or blue dye.The space above the liquid is a mixture of nitrogen and the vapour of the liquid.The range of usefulness of the thermometer is set by the boiling point of the liquid used.
Tuesday, July 12, 2011
CLASS-VII
CHEMICAL SUBSTANCES AND PROCESSES
WORKSHEET-1
Q1. Fill in the blanks:
a) Burning of wood in air converts it into ___________ and __________.
b) Copper articles get coated with a green substance on exposure to ___________.
c) Chemical name of common salt is ____________________.
d) Chemical name of limestone is ____________________.
e) CaO is also called ________________.
f) Combination of nitrogen and hydrogen gas gives ___________ gas.
g) __________ is the chemical formula of glucose.
Q2. Name any two:
a) positive ions
b) negative ions
Q3. Observe the diagram carefully and answer the following questions:
( for diagram, refer worksheet given in class)
a) Name the reaction.
b) Write the chemical equation for the reaction.
c) Name the element which deposits as a brown coating.
Q4. What happens when electric current is passed through water? Write chemical equation also.
Q5. Write the chemical formula of the following:
a) Magnesium sulphate
b) Calcium oxide
c) Aluminium hydroxide
d) Zinc phosphate
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