P1 Formulas and Questions. There are 7 formulas you may get in P1

wave speed = frequency × wavelength v = f × λ

1. A water wave has a wavelength of 8m and a frequency of 4. 5Hz 1. A water wave has a wavelength of 8m and a frequency of 4.5Hz. What is its wavespeed?

1. A water wave has a wavelength of 8m and a frequency of 4. 5Hz 1. A water wave has a wavelength of 8m and a frequency of 4.5Hz. What is its wavespeed? V = f × λ = 4.5Hz x 8m (1) = 36m/s (1)

2. A sound wave has a frequency of 6 2. A sound wave has a frequency of 6.5kHz and it travels at a speed of 330m/s. What is its wavelength?

2. A sound wave has a frequency of 6 2. A sound wave has a frequency of 6.5kHz and it travels at a speed of 330m/s. What is its wavelength? λ = v ÷ f = 330m/s ÷ 6500Hz (1) = 0.05m (1)

3. A wave on the sea travels at 5m/s and has a wavelength of 6m 3. A wave on the sea travels at 5m/s and has a wavelength of 6m. What is its frequency?

3. A wave on the sea travels at 5m/s and has a wavelength of 6m 3. A wave on the sea travels at 5m/s and has a wavelength of 6m. What is its frequency? f = v ÷ λ = 5m/s ÷ 6m (1) = 0.8Hz (1)

4. Radio 1 is a frequency of 97MHz (c) and it travels at the speed of light which is 3 x 108 m/s. What is its wavelength?

4. Radio 1 is a frequency of 97MHz (c) and it travels at the speed of light which is 3 x 108 m/s. What is its wavelength? λ = v ÷ f = 3 x 108 m/s ÷ 97 x 106 m/s (1) = 3.1 m (1)

5. A gamma wave has a wavelength of 6 x 10-8m and it travels at the speed of light (3 x 108 m/s). What is its frequency?

5. A gamma wave has a wavelength of 6 x 10-8m and it travels at the speed of light (3 x 108 m/s). What is its frequency? f = v ÷ λ = 3 x 108 m/s ÷ 6 x 10-8m (1) = 5 x 1015 Hz (1)

6. A light wave travelling down an optic fibre has a wavelength of 5 x 10-7 m and a frequency of 4.4 x 1014Hz. What is its speed?

6. A light wave travelling down an optic fibre has a wavelength of 5 x 10-7 m and a frequency of 4.4 x 1014Hz. What is its speed? V = f × λ = 4.4 x 1014 Hz x 5 x 10-7m (1) = 2.2 x 108 m/s (1)

wave speed =distance v = x time t

7. A wave travels 35m in 7 seconds. What is its speed?

7. A wave travels 35m in 7 seconds. What is its speed? v = x ÷ t = 35m ÷ 7s (1) = 5m/s (1)

8. A wave travels at 2. 9km/s for 3minutes 8. A wave travels at 2.9km/s for 3minutes. How far does it travel in metres?

8. A wave travels at 2. 9km/s for 3minutes 8. A wave travels at 2.9km/s for 3minutes. How far does it travel in metres? x = v × t = 2900m/s x 180s (1) = 522 000m (1)

9. How long does it take a wave travelling at 3cm/s to travel a distance of 9.6m?

9. How long does it take a wave travelling at 3cm/s to travel a distance of 9.6m? t = x ÷ v = 9.6m ÷ 0.03m/s (1) = 320s (1)

electrical power = current × potential difference P = I × V P is the symbol for power Units: Watts, W I is the symbol for current Units: Amps, A V is the symbol for potential difference Units: Volts, V.

10. A kettle has a power of 2000W and the p. d. across it is 230V 10. A kettle has a power of 2000W and the p.d. across it is 230V. What is the current through it?

10. A kettle has a power of 2000W and the p. d. across it is 230V 10. A kettle has a power of 2000W and the p.d. across it is 230V. What is the current through it? I = P ÷ V = 2000W ÷ 230v (1) = 8.7A (1)

11. What is the p.d. across an 11W bulb when the current through it is 0.05A?

11. What is the p.d. across an 11W bulb when the current through it is 0.05A? V = P ÷ I = 11W ÷ 0.05A (1) = 220V (1)

12. An X –box has a p.d. across it of 230V and the current through it is 0.2A. What power is it transferring?

12. An X –box has a p.d. across it of 230V and the current through it is 0.2A. What power is it transferring? P = I x V = 0.2A x 230v (1) = 46W (1)

13. A theatre lighting system works from 400V and has a power of 9kW 13. A theatre lighting system works from 400V and has a power of 9kW. What current is it using?

13. A theatre lighting system works from 400V and has a power of 9kW 13. A theatre lighting system works from 400V and has a power of 9kW. What current is it using? I = P ÷ v = 9000W ÷ 400v (1) = 22.5A (1)

Power must be measured in KILOWATTS (kW) Power must be measured in KILOWATTS (kW). Time must be measured in HOURS.

14. A 2kW fire is on for 6 hours & 1 kilowatt-hour costs 12p 14. A 2kW fire is on for 6 hours & 1 kilowatt-hour costs 12p. How much does the electricity cost? kWhrs = 2kW x 6hrs (1) = 12kWhrs (1) Cost = 12kWhrs x 12p = 144p (1)

15. A 150W T. V is on for 13 hours & 1 kilowatt-hour costs 12p 15. A 150W T.V is on for 13 hours & 1 kilowatt-hour costs 12p. How much does the electricity cost?

15. A 150W T. V is on for 13 hours & 1 kilowatt-hour costs 12p 15. A 150W T.V is on for 13 hours & 1 kilowatt-hour costs 12p. How much does the electricity cost? kWhrs = 0.15W x 13hrs (1) = 1.95kWhrs (1) Cost = 1.95kWhrs x 12p = 23.4p (1)

16. A 700W hairdryer is on for 8 minutes and 1 kilowatt-hour costs 15p 16. A 700W hairdryer is on for 8 minutes and 1 kilowatt-hour costs 15p. How much does the electricity cost?

16. A 700W hairdryer is on for 8 minutes and 1 kilowatt-hour costs 15p 16. A 700W hairdryer is on for 8 minutes and 1 kilowatt-hour costs 15p. How much does the electricity cost? kWhrs = 0.7kW x 8/60hrs (1) = 0.093kWhrs (1) Cost = 0.093kWhrs x 15p = 1.4p (1)

17. A 50W fridge is on for 5 days and 1 kilowatt-hour costs 9p 17. A 50W fridge is on for 5 days and 1 kilowatt-hour costs 9p. How much does the electricity cost?

17. A 50W fridge is on for 5 days and 1 kilowatt-hour costs 9p 17. A 50W fridge is on for 5 days and 1 kilowatt-hour costs 9p. How much does the electricity cost? kWhrs = 0.05kW x 5 x 24hrs (1) = 6kWhrs (1) Cost = 6kWhrs x 9p = 54p (1)

power =energy used P = E time taken t P is the symbol for power Units: Watts, W E is the symbol for energy used Units: Joules, J t is the symbol for time taken Units: seconds, s.

18. A lawnmower uses 5000J of energy in 32s. What is its power?

18. A lawnmower uses 5000J of energy in 32s. What is its power? P = E ÷ t = 5000j ÷ 32s (1) = 156W (1)

19. A toaster has a power of 350W and is on for 2 minutes 19. A toaster has a power of 350W and is on for 2 minutes. How much energy does it use?

19. A toaster has a power of 350W and is on for 2 minutes 19. A toaster has a power of 350W and is on for 2 minutes. How much energy does it use? E = P x t = 350W x 120s (1) = 42000j (1)

20. How long does a 5kW car engine take to use 6 MJ (6 x 106 J) of energy?

20. How long does a 5kW car engine take to use 6 MJ (6 x 106 J) of energy? t = E ÷ P = 6 x 106 j ÷ 5000W (1) = 1200s (1)

Chemical energy in fuel 30 000J Useful Kinetic energy 7 500J Wasted heat 22 000J Chemical energy in fuel 30 000J Useful Kinetic energy 7 500J Wasted sound energy efficiency = (useful energy transferred by the device) x 100% (total energy supplied to the device)

21. How much energy is wasted as sound?

21. How much energy is wasted as sound? Total Energy Input = Total Energy Output 30000j = 7500j + 22000j + sound energy (1) sound energy = 30000j – 7500j – 22000j (1) = 500j (1)

22. What is the efficiency of the car?

22. What is the efficiency of the car? efficiency = (useful energy transferred by the device) x 100% (total energy supplied to the device) = 7500J ÷ 30000j x 100% (1) = 25% (1)

23. A motor bike is 30% efficient 23. A motor bike is 30% efficient. If the total energy supplied to it is 6000J, how much energy is usefully transferred to it?

23. A motor bike is 30% efficient 23. A motor bike is 30% efficient. If the total energy supplied to it is 6000J, how much energy is usefully transferred to it? efficiency = (useful energy transferred by the device) x 100% (total energy supplied to the device) 30% = Useful Energy ÷ 6000j x 100% (1) Useful Energy ÷ 6000j = 30% ÷ 100% = 0.3 Useful Energy = 0.3 x 6000j = 1800J (1)

primary voltage = number of turns on primary coil Vp = Np secondary voltage number of turns on secondary coil Vs Ns

24. A transformer has a primary voltage of 20V 24. A transformer has a primary voltage of 20V. The number of turns on the primary coil is 300 and on the secondary coil there are 2400 turns. What is the secondary voltage?

24. A transformer has a primary voltage of 20V 24. A transformer has a primary voltage of 20V. The number of turns on the primary coil is 300 and on the secondary coil there are 2400 turns. What is the secondary voltage? Vp = Np Vs Ns 20v = 300 Vs 2400 Vs = 20v x 2400 x 300 = 160v

25. A transformer has a secondary voltage of 900V 25. A transformer has a secondary voltage of 900V. The number of turns on the primary coil is 150 and on the secondary coil there are 750 turns. What is the primary voltage?

25. A transformer has a secondary voltage of 900V 25. A transformer has a secondary voltage of 900V. The number of turns on the primary coil is 150 and on the secondary coil there are 750 turns. What is the primary voltage? Vp = Np Vs Ns Vp = 150 900 750 Vp = 150 x 900 = 180V 750

26. A transformer has a primary voltage of 230V and a secondary voltage of 30V. If the primary has 700 turns, how many turns has the secondary got?

26. A transformer has a primary voltage of 230V and a secondary voltage of 30V. If the primary has 700 turns, how many turns has the secondary got? Np = Vp Ns Vs 700 = 230v Ns 30v Ns = 700 x 30v / 230v Ns = 91turns

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