##
__REFLECTION AT CURVED SURFACES & REFRACTION AT CURVED SURFACES:__

1. Magnification : m = -v/u or m=hi/ho

2. Mirror formula, 1/f = 1/u + 1/v

3. focal length f = R/2

4. Lens formula 1/f = 1/v - 1/u

5. Lens makers fomula : 1/f = (n-1) (1/R1 - 1/R2)

6. The relation between refractive indices of media, object distance, image distance, and radius of curvature is given by :

n2/v - n1/u = (n2-n1)/R

7. In case of plane mirrors, R, F are infinity, then the power is equal to zero.

n2/v = n1/u

8. The refractive index of prism is

n = sin{[A+D]/2}/SIN [A/2]

9. Speed of wave is , v = Frequency x wavelength

10. snell's law is n1sini = n2sinr

11. A + d = i1 + i2

b>PROBLEM 3:

## PROBLEMS IN PHYSICS - REFLECTION AT CURVED SURFACES

**PROBLEM 1:****Where is the image formed when 8 cm tall object is placed at 20 cm. in front of a concave mirror with focal length 5 cm. Find out the size of the image also.**

**PROBLEM 2:**

**A 10 cm tall object is placed in front of a convex mirror of focal length 15 cm, Find out the image distance and write its characteristics .**

b>PROBLEM 3:

**10 cm focal length concave mirror is placed at 40 cm, from a wall. Calculate the object distance such that its image is formed on the wall.**

**PROBLEM 4:**

**In front of 15 cm focal length concave mirror, an object is placed at 30 cm, if the object is displaced through 10 cm towards mirror, calculate by how much distance the image is displaced?**

**PROBLEM 5:**

**The image is formed behind the mirror, at a distance of 10 cm, when an object is placed at 20 cm in front of it. Identify the type of mirror used and also calculate the focal length.**

## ELECTRICITY:

1. Electric current i = Q/t

2. Potential difference, V = W/Q

3. Resistance R = (Resistivity * length)/Area

4. Resistance R=V/I

5. Electric power P = V * I

6. P=V2/R

7. CONDUCTIVITY = 1/Resistivity

8. Resistors connected in series, R = R1 + R2 + R3 +.....

9. Resistors connected in parallel 1/R = 1/R1 + 1/R2 + 1/R3.......

MODEL PROBLEMS :

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1. If you are using an electric lamp and it lights for 6 hours and the current drawn by it is 0.24 A. Then calculate the amount of charge flowing through the lamp.

2. A circuit consists of five resistors, 10 ohm, 20 ohm, 30 ohm, 40 ohm, 50 ohm, your aim is to decrease the effective resistance using the given resistors, then how do you connect them and calculate the resultant resistance.

3. Suppose that you are using a water heater to heat the water having resistance of 90 ohm, and connected to 240 v. p.d. Determine the current flowing through the water heater.

4. Calculate the number of units when 50w, 60w, 80w electrical appliances are being used daily for 2 hours for 30 days.

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