Transcript File - singhscience

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.
What is its wavespeed?
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
6.5kHz and it travels at a speed
of 330m/s. What is its wavelength?
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.
What is its frequency?
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
0.8Hz
(1)
(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 107 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
time
v=x
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
5m/s
(1)
(1)
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. How far does it travel in
metres?
x
=
=
=
v×t
2900m/s x 180s
522 000m
(1)
(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
320s
(1)
(1)
electrical power = current × potential difference
P=I×V
P is the symbol for power
I is the symbol for current
V is the symbol for potential difference
Units: Watts, W
Units: Amps, A
Units: Volts, V.
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.
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
=
=
=
IxV
0.2A x 230v
46W
(1)
(1)
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.
What current is it using?
I
=
=
=
P÷v
9000W ÷ 400v (1)
22.5A
(1)
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. 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. How much
does the electricity cost?
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. How much does the electricity
cost?
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. How much
does the electricity cost?
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
6kWhrs (1)
Cost =
=
6kWhrs x 9p
54p
(1)
(1)
power =energy used
time taken
P=E
t
P is the symbol for power
E is the symbol for energy used
t is the symbol for time taken
Units: Watts, W
Units: Joules, J
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
156W
(1)
(1)
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. How much
energy does it use?
E
=
=
=
Pxt
350W x 120s
42000j
(1)
(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)
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)
(total energy supplied to the device)
x 100%
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
sound energy
= 30000j – 7500j – 22000j
= 500j
(1)
(1)
(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. If
the total energy supplied to it is
6000J, how much energy is usefully
transferred to it?
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
secondary voltage
= number of turns on primary coil
number of turns on secondary coil
Vp
Vs
=
Np
Ns
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. 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 =
Vs
300
2400
Vs
20v x 2400 x 300
=
=
160v
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. 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
=
900
Vp
=
150
750
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
Ns
700
Ns
Ns
Ns
=
Vp
Vs
=
=
=
230v
30v
700 x 30v / 230v
91turns
20.