IMPORTANT PHYSICS PROBLEMS
ELECTRICITY
1. Observe the below table. Which of the below listed electrical appliances consumes more energy?
a)
TV.
P = 250W = 0.25kW
t = 4h
E = P × t
E = 0.25 × 4 = 1kWh
Toaster.
P = 1200W = 1.2kW
t = 1h
E = P × t
E = 1.2 × 1 = 1.2kWh
→ Toaster consumes more energy.
2. 2 Ω and 4 Ω resistors are connected in parallel. If 6 Ω resistor is used in place of 4 Ω, then find the difference between the difference between the total resistance obtained in both of these arrangements.
Ans:
R₁ = 2 Ω, R₂ = 4 Ω
1/R = 1/R₁ + 1/R₂
= 1/2 + 1/4 = 8/6 = 1.33 Ω
If 6 Ω instead of 4 Ω:
1/ R = 1/2 + 1/6 = 12/8 = 1.5 Ω
Difference = 1.5 – 1.33 = 0.17 Ω
3. A 350W bread toaster is used 6 hours a day. A 250W iron box is used 4 hours a day. If these appliances are used for 30 days, then calculate the total cost of the energy consumption at the rate of Rs. 4 for 1kWh.
Ans:
Toaster:
P = 350W = 0.35KW
t = 6h × 30 days = 180h
E = P × t
E = 0.35kW × 180h = 63kWh
350W × 6h × 30d = 63,000 Wh = 63 kWh
Iron box:
P = 250W = 0.25kW
t = 4h × 30d = 120h
E = P × t
E = 0.25kW × 120h = 30kWh
Total = 63kWh + 30kWh = 93 kWh
Cost = 93 × ₹4 = ₹372
4. A fan having the power 880W is connected to a source of potential difference 220V in an electric circuit. Calculate the electric current and the electric resistance of this circuit.
Ans:
Fan:
P = 880W
V = 220V
I = P/V = 880/220 = 4 A
R = V/I = 220/4 = 55 Ω
5. An electric motor receives 10A electric current from 220V electric source. Find the power of motor.
Ans:
Given:
I = 10A
V = 220V
P = ?
P = V × I
P = 220 × 10 = 2200W
6. Observe the diagram of below given electric circuit. Find the total resistance and the total current of the circuit.
7. An electric fan rated 50 W is used for 6 hours in a day. What is the cost of the energy it consumes for 30 days at Rs.4 per 1kWh?
LIGHT REFLECTION AND RETRACTION
1. An object is placed perpendicular to principal axis of a convex lens of focal length 20cm. If the distance of image is to be 60cm, then at what distance the object is to be placed from the lens?
Ans:
Given:
Focal length (f) = +20cm
Image distance (v) = +60cm
Object distance (u) =?
The object is to be placed at a distance of 30cm from the lens.
2. The object distance and image distance of a lens are -30cm and -10 cm respectively. Decide the type of lens and nature of image
Ans:
Given
Object distance (u): -30cm
Image distance (v): -10cm
Since the focal length (f) is negative (f = -15cm), the lens is a Concave Lens.
The magnification for a lens is given by:
A positive magnification indicates that the image is Erect and virtual image
magnification is less than 1. This means the image is Diminished.
No comments:
Post a Comment