1. P3 Calculations

2. The speed of sound in the steel is 6000m/s. What is the distance to the flaw? s = v x t s = 6000 x (5 x 0.000005)/2 s = 0.075m Remember to halve the time

3. Calculate the magnification of the lens ? M= Image Height Object Height M= 18/6 M = 3

4. Calculate the weight of the boy Clockwise Moment = Anticlockwise moment 360 + 1.6W = 960 1.6W = 600 W = 375 N

5. If the pendulum takes 20 seconds to complete 10 swings what is its frequency ? Time period = 2 seconds f= 1/T f=1 / 2 = 0.5 Hz

6. What is the force exerted by the large cylinder? Pressure on small cylinder = F/A = 20/5 = 4N/cm 2 Force = P x A = 4 x 25 = 100 N Area = 5 cm 2 Area = 25 cm 2 Force = 20N So Pressure on large cylinder = 4N/cm 2

7. Vp= Np Vs= Ns In the National Grid, very large step-up transformers link power stations to the transmission cables. A transformer used for this purpose has 800 turns on its primary coil and 12 800 turns on its secondary coil. The p.d. (potential difference) across its primary coil is 25 kV. Calculate the p.d. across its secondary coil 25000 = 800 Ns 12800 25000 = 0.0625 Ns 25000 = 0.0625 Ns 25000 = Ns 0.0625 400,000 = Ns

8. Calculate the refractive index of glass Refractive index = sini sin r Refractive index = sin60 o sin34.5 o Refractive index = 0.87 / 0.57 Refractive index = 1.52

9. Calculate the refractive index of glass Critical angle = 42 o Refractive index = 1 sin c Refractive index = 1 sin 42 o Refractive index = 1.49

10. What is the power of a convex lens of focal length 20cm ? Power = 1 f Power = 1 = +5 Diopters 0.2 Refractive index = 1.49

11. What is the power of a concave lens of focal length 20cm ? Power = 1 f Power = 1 = -5 Diopters 0.2 Refractive index = 1.49

12. If the primary current is 2.5 A what is the current in the secondary? Vp x Ip= Vs x Is 10 x 2.5= 20 x Is 25 = 20 Is 25 = Is 20 1.25A = Is