Download Questions - Science @ St John`s

Questions
Q1.
Complete the sentence by putting a cross (
An electric current is the rate of flow of
) in the box next to your answer.
(1)
A
B
C
D
atoms
charge
voltage
watts
Q2.
The diagram shows a simple generator connected to a lamp.
The magnet is made to spin at a steady speed.
The ammeter gives a reading of 1.5 A.
The voltmeter gives a reading of 6 V.
(i) Calculate the output power of the generator.
(2)
..............................................................................................................................................
(ii) State two changes to the design of the generator that would give a larger output power for the same
speed of rotation.
(2)
..............................................................................................................................................
..............................................................................................................................................
(iii) This generator supplies an alternating current (AC) to the lamp.
Other types of generators supply a direct current (DC).
Describe the difference between charge movement in a direct current and in an alternating current.
(2)
..............................................................................................................................................
..............................................................................................................................................
Q3.
Alternating current and its uses
The diagram shows a generator producing an alternating voltage.
(a) Draw one straight line from each letter to its correct label.
(2)
(b) The generator is connected to a lamp.
The current in the lamp is alternating.
(i) Which of these is an alternating current?
Put a cross ( ) in the box next to your answer.
(1)
(ii) The generator is turned faster.
Explain what happens to the lamp.
(2)
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
(c) A larger generator produces a current of 2 A at a voltage of 12 V.
Calculate the electrical power generated.
State the unit.
(3)
power generated =........................... unit =...........................
(d) Transformers are designed to use alternating current.
Describe what change happens when a step-up transformer is used.
(2)
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
Q4.
The photograph shows Alan’s bike-powered generator.
Alan pedals at a steady speed.
(i) The output voltage of the generator is 12.3 V.
The output current is 8.00 A.
Calculate the output power of the generator.
(2)
output power = ............................................... W
(ii) Alan supplies 15 600 J to the generator in 120 s.
Calculate the input power to the generator.
(2)
input power = .............................................. W
Q5.
A television has a power of 400 W.
The cost of 1 kW h of electrical energy is 15p.
Calculate the cost of using the television for 10 hours.
(3)
..............................................................................................................................................
Q6.
A solar panel generates direct current.
(i) Describe the difference between direct current and alternating current.
(2)
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
(ii) The output from the solar panel is 60 V.
State why a transformer cannot be used to increase this voltage.
(1)
..............................................................................................................................................
..............................................................................................................................................
Q7.
A LED lamp has a power rating of 3 W.
The voltage across the lamp is 12 V.
Calculate the current in the lamp.
(3)
current in the lamp =. . . . . . . . . . . . . . . . . . . . .A
Q8.
Scientists say that graph 1 shows an alternating current while graph 2 shows a direct current.
The two graphs differ in several ways.
State the difference between the currents which makes one alternating and the other direct.
(1)
..............................................................................................................................................
..............................................................................................................................................
Q9.
A homeowner fits a solar panel to her roof.
The cost of the solar panel is £4800.
The solar panel supplies an average of 800 kW h of electrical energy to the National Grid each year.
The homeowner is paid 40p for each kW h of energy supplied to the National Grid.
Calculate the payback time for the solar panels by selling energy to the National Grid.
(3)
payback time = ......................................................... years
Mark Scheme
Q1.
Answer
B
Acceptable
answers
Mark
(1)
charge
Q2.
Answer
(i)
Substitution (1)
1.5 × 6
Evaluation (1)
9 (W) Ignore any
unit given by
candidate.
(ii)
 More turns on the
coil (1)
 More
powerful/stronger
magnet(s) (1)
(iii)
A description
including
 in one direction
only for DC (1)
 reversing
direction for AC (1)
Acceptable
answers
Power of 10 error
max 1 mark Give full
marks for correct
answer with no
working shown
Mark
(2)
Wrap coils on iron
(core/former)/ more
coils/twists/loops.
Bigger coil is
insufficient. More
magnets.
Bigger/larger magnet
is insufficient.
(2)
Ignore increase
speed of rotation
(2)
'DC goes straight' is
insufficient AC
switches/changes
direction OR moves
to and fro 'AC goes
different ways' is
insufficient.
Diagram with labelled
arrows could get 2
marks.
Q3.
Question
Number
(a)
Answer
Question
Number
(b)(i)
Question
Number
(b)(ii)
Answer
Acceptable answers
(2)
Mark
B
Answer
Acceptable answers
(1)
Mark
Question
Number
(c)
Question
Number
(d)
Acceptable answers
Mark
More than one line
bfrom either P or Q
(or both) loses the
mark for that box
An explanation
linking the following
• increased
brightness (1)
• (due to) increased
voltage (1)
Answer
‘fuses’ / ‘blows’ / gets
hotter
Acceptable answers
(1)
Mark
substitution (1) 2 x 12 Give full marks (2) for
evaluation (1) 24 unit correct answer, no
(1)W
working (accept bald
2.4 for substitution) =
1 watt(s), AV, VA, J/s
If only one number
and one unit their
position is immaterial
otherwise, mark the
number in the power
generated space and
the unit in the unit
(3)
space
Answer
Acceptable answers Mark
A description
including the
following • voltage
(1) • increases (1)
current decreases
(ignore speed of
current) Accept for 1
mark • increases
current AND reduces
voltage • voltage
higher and bigger
current/power
• power decreases
‘it’
increases/decreases
=0
(3)
Q4.
Question
Number
(i)
Question
Number
(ii)
Answer
Acceptable answers
substitution (1)
(output power =) 8.00
× 12.3 evaluation (1)
98.4 (W)
Answer
give full marks for
correct answer, no
working
substitution (1) (input
power =) 15600 ÷
120 evaluation (1)
130 (W)
give full marks for
correct answer, no
working
Answer
Conversion
0.4
(kW)
(1)
Substitution
0.4 × 10 ×15
(p)
(1)
or
0.4 × 10 × 0.15 (£)
Evaluation
60(p) or
£0.6
(1)
Acceptable
Mark
answers
(3)
give marks
for correct answer,
no working
60(p) or
£0.6
(3)
60,000(p) or
£600
(2)
6 to any other power
of 10
(1)
(400/40/4) × 10 ×
(15/0.15) gains one
mark if no mark can
be awarded for
evaluation.
Answer
Acceptable answers
a description
including the
following • direct
current (the flow of
charge) is only in one
direction (1)
• alternating current
(the flow of charge
periodically) changes
/ reverses direction /
eq (1)
Answer
d.c stays
positive/negative
only goes positive
and negative
any one of the
following
It is not alternating
(1)
/ direct current
Acceptable answers
Mark
(2)
Mark
(2)
Q5.
Q6.
Question
Number
(i)
Question
Number
(ii)
Acceptable answers
Mark
(2)
Mark
• transformers only
change alternating
voltages / currents
• transformers will
not work with direct
current
Q7.
Answer
Acceptable
Mark
answers
substitute (1)
Subst. and transform.
3 = I × 12
either order
transformation (1)
1 mark only can be
I = 3 ÷ 12 evaluation scored for correct
(1)
substitution after
0 .25 (A) Ignore any incorrect
unit given by
transposition. Accept
candidate
any number of sig.
figs. that rounds to
0.25 (A) 250 mA
gains 3 marks give
full marks for correct
answer, no working
2.5 × any other
power of ten = 2
marks eg 25 (A)
(3)
gains 2 marks
Q8.
Question
Number
Answer
Acceptable answers
Mark
alternating current
can take positive and
negative values RA
(1)
a.c. above and
below zero /the line
a.c. goes one way
and then the other
RA
(1)
Answer
Acceptable answers
Mark
substitution (1) 800 ×
0.4 / 800 × 40
evaluation of
payment (1) (£)320 /
32000 (p) evaluation
of payback time (1)
15 (years)
4800 / 0.4 = 12000
Kwh (to be sold)
takes 12000 / 800
years substitution
and transposition can
be in either order
allow power of 10
error in 15 for (2) give
full marks for correct
(3)
answer, no working
Q9.
Question
Number