unit 3 Flashcards
minimise parallax error when timing the ball bearing
as it falls through a fixed distance in the oil?
Ensure that the observer is at eye level with the ball bearing.
NOT
- Use a metre rule rather than the scale on the measuring cylinder.
- Use two parallel rubber bands around the measuring cylinder to indicate the
fixed distance. - Start and stop the clock as the middle of the ball bearing passes through the
start and finish points.
e.m.f. of the battery
V vs A graph
intercept with the potential difference axis
determine the percentage loss of kinetic energy after a ball dropped
from a fixed height has bounced once on a hard surface.
assumption: that the initial gpe of the ball will all be converted to ke just before the ball hits the hard surface.
1. Describe an experiment which could be carried out to achieve this.
2. State one precaution to improve the accuracy of the results.
rough structure
Means of measuring height (1)
• Means of determining speed (1)
• Equates (final) GPE with (final) KE (1)
• Method to determine KE after bounce (1)
• Description of appropriate experimental method (1)
• States that mass cancels OR mass stays the same OR mass
measured OR mass known (1)
•
• Indication of how (percentage) energy loss will be determined
determine the percentage loss of kinetic energy after a ball dropped
from a fixed height has bounced once on a hard surface.
assumption: that the initial gpe of the ball will all be converted to ke just before the ball hits the hard surface.
1. Describe an experiment which could be carried out to achieve this.
2. State one precaution to improve the accuracy of the results.
ANS
Drops ball of known mass vertically from known height
• Determines height of bounce using a metre rule
• States mg∆h = 1/2mv^2
- % loss in KE = loss in PE/ initial PE x 100%
- Precaution: make measurement of height of bounce at eye level
Draw a circuit diagram to show the circuit he should use to find the resistance of a fixed length of constantan wire.
apparatus
includes a length of constantan wire, an ammeter, a voltmeter, a variable resistor and a
micrometer.
Ammeter in series and voltmeter in parallel
use a range of current values to plot a graph of p.d. against current.
how to use the graph to determine a value for the resistance R of the length of wire.
Find gradient which is R (1)
Explain how plotting a graph should improve his result
- Graph enables an average result to be taken (1)
- Graph will show anomalies(1)
- Graph will show if resistance changes (1)
State and explain what additional instrument he should use to measure the length l of
the wire
Metre rule/tape(1)
• Longer length so measurement to nearest mm appropriate (1)
• [allow to nearest ½ mm]
State what further measurement needed to take to determine the
resistivity of the wire
and
Show how to use these measurements to calculate a value for the
resistivity of constantan
Diameter (1)
- Find area using A = πd^2/4 or A = πr^2
- Calculate ρ using R =ρl/A
experiment to compare the behaviour of two
wires when forces are applied to them.
first is to find the constant k in the equation
F = k∆x for each wire.
plan
Vertical length of wire with masses on end OR horizontal wire
with masses over pulley (1)
• Measure extension (1)
• Further detail (1)
• e.g. use of mark on wire OR use of F = k∆x
• OR extension = final – initial length OR comparison of
wires
experiment to compare the behaviour of two
wires when forces are applied to them.
State one variable which would have to be kept constant to make this a fair test.
State and explain one safety precaution they would need to take.
(Initial) length of wires (1)
- Use of goggles OR means of catching/avoiding falling masses
- Protection (of eyes) from snapping wire OR protection of feet/floor from falling masses (1)
F = k∆x for each wire.
The wires are going to be used to hang pictures on a wall in an art exhibition.
Explain why knowing a value for k may be useful.
k chosen so that wire wont stretch or break for a given
picture
Criticise this set of measurements.
Inconsistent precision of timing(1) • Lengths only recorded to nearest 10 cm (1) • Only 10 oscillations timed (1) • Too few values(1) • No repeats(1) • Small range(1)
The multimeter is used to measure the potential difference across the 100 : resistor in
the circuit.
Which is be the best setting to use?
20 V
investigating the variation in the emf generated by a solar cell with light intensity.
varies the distance between the solar cell and a lamp.
Which is the independent variable?
Which is the measured dependent variable?
independent variable
- distance
dependent variable
-emf
