Practical Based Questions

Question 1

describe an experiment to determine the resistivity ρ of the material of the resistance wire. Your description should include
• the measurements taken
• the instruments used to take the measurements
• how the measurements are used to determine the resistivity of the material.

(6 marks)

Answer 1

ρ= (RA)/L
R = resistance, L = length and A = (cross-sectional) area 
(ρ = resistivity is given in the question)

Any four from:
Measure the length of the wire using a ruler
Measure the diameter of the wire using a micrometer \ vernier (calliper)

Calculate the (cross-sectional) area using A = πr^2 \ A = πd^2/4
Calculate the resistance (of the wire) using R = V/I
Repeat experiment for different lengths \ current \ voltage \ diameter (to get an average)
Plot a graph of R against L. The gradient = ρ/A.
(Or Plot V against I. The gradient is ρL/A)

Question 2

Many cars are fitted with Global Positioning System (GPS) devices.
Describe how geostationary satellites are used to track the location of cars on the Earth’s surface.

Answer 2

Radio waves or microwaves transmitted from satellites. There is a delay time between signal from satellite to position of GPS device. Distance between satellite and GPS device calculated by delay time x speed of light. Trilateration / intersecting circles / spheres (used to locate position of car)

Question 3

One of the safety features in a car is the air bag for the driver. Briefly describe how the air bag is triggered and how it minimises the impact force on the driver.

Answer 3

Large deceleration / rapid decrease in speed (triggers the air bag)
Prevent collision with steering wheel / windscreen/ dashboard
Time (for stopping) is more / distance (for stopping) is more
Smaller deceleration / acceleration (of person)

Question 4

Describe in terms of the forces acting on the driver how wearing a seat belt and having an airbag in a car can help to protect the driver from injury in a head on collision.

Answer 4

Prevents the driver from hitting the steering wheel / windscreen
Deflates quickly to prevent whiplash
Increases the time/distance to stop
Decreases the (impact) force on the driver
Much wider area of the bag reduces the pressure

Question 5

State factors that affect the braking distance of a car. Describe how each factor affects the braking distance.

Answer 5

speed, mass, condition of tyres, condition of brakes, condition of road, gradient of road
• Greater speed means greater distance Or distance ∞ speed^2
• Greater mass means greater distance Or distance ∞ mass
• Worn tyres / brakes implies less friction therefore greater distance
• Wet / slippery / icy road means less friction therefore greater distance
• Uphill means shorter distance

Question 6

Describe an experiment to determine the centre of gravity of a metal plate

Answer 6

1. (Suspend plate from a point and then) mark a vertical line on the plate
2. Plumb line / ‘pendulum’ (used to find the vertical line)
3. Hang from another point / place (and draw another vertical line)
4. Where the lines intersect gives position of centre of gravity

Question 7

Describe the experiments Galileo carried out which overturned Aristotle’s ideas of motion.

Answer 7

Galileo dropped different mass balls / rolled different mass balls (down a ramp)
Balls hit the ground / reached the bottom (of ramp) at the same time
(Galileo -) All objects fall with the same acceleration
(Aristotle -) Heavy / massive objects fall faster / quicker than light objects

Question 8

A student conducts an experiment to estimate the acceleration g of free fall by dropping a heavy metal ball from a high wall into a sandpit below. Describe how this student can estimate the acceleration g of free fall. Your description should include:
• the measurements taken
• the instruments used to take the measurements
• how the measurements are used to estimate g
• an explanation of why the value for g is only an estimate

Answer 8

Measurements:
height (of wall)
time (of fall)

Instruments:
ruler / tape (measure)
stopwatch / timer / clock /video

using g= 2s/t^2

g is an estimate because
 air resistance / drag ignored
 parallax problems with ‘landing time’
 starting / stopping the clock

Question 9

Explain how you would determine experimentally the e.m.f. E and internal resistance r of the charged cell. Include a circuit diagram with meters and a variable load resistor.
In your answer you should state how the data collected is used to determine the values of E and r.

Answer 9

1.cell across variable resistor R ammeter in series and voltmeter
in parallel across R or cell
2.Take (set of) readings of V and I for different positions/values
of the variable resistor
3.plot a graph of V against I
4.(find) y-intercept = E
5.(find) the gradient of the V against I graph which equals the
internal resistance in magnitude
or 4 or 5 take one pair of values of V,I and substitute
into equation E = V + Ir to find r or E

Question 10

A physical quantity is also conserved in the photoelectric effect. Describe and explain the photoelectric effect.
In your answer you should link the description to the conservation of this quantity

Answer 10

A photon is absorbed by an electron (in a metal surface)causing electron to be emitted (from surface). Energy is conserved (in the interaction).Only photons with energy/frequency above the work function energy/threshold frequency will cause emission. (energy of photon) = (work function of metal) + (maximum possible kinetic energy of emitted electron)
work function energy is the minimum energy to release an electron from the surface.
Number of electrons emitted also depends on light intensity. Emission is instantaneous

Question 11

A student wants to carry out an experiment to determine the input power to a small electric motor without using electrical meters. The motor is used to lift light loads. The efficiency of the motor is 15%. Describe how this student can determine the input power to the motor. Your description
should include:
• the measurements taken
• the instruments used to take the measurements
• how the measurements are used to determine the input power to the motor.

Answer 11

Any one from:
 Mass obtained using a balance / scales
 Weight / load obtained using a newtonmeter / spring balance
 Distance / height obtained using a ruler / metre stick /measuring tape
Time obtained using a clock / (stop)watch / timer or lightgate and timer or light-gate and data-logger

(output power =) ‘mass x g x distance’/time or ‘weight x distance/time’ or ‘weight x speed’
input power = output power/0.15

Question 12

You are given a spring, a metre rule and a 100 g mass. Describe how you would determine the force constant k of the spring.

Answer 12

Place the 100 g mass on the spring / hang the 100 g mass from the spring
Determine the extension / compression of the spring (using a ruler)
force constant = 0.98(1)/extension

Question 13

Describe how you can use apparatus to determine the Young modulus of the metal.
The measurements to be taken:
The equipment used to take the measurements:
How you would determine Young modulus from your measurements:

(8 marks)

Answer 13

Measurement:
 Diameter
 original / initial length (Not: final length)
 extension / initial and final lengths
 weight / mass

Equipment:
 Micrometer / vernier (calliper) (for the diameter
of the wire)
Any two from:
 Ruler / (metre) rule / tape measure (for
measuring the original length / extension)
 Travelling microscope (for measuring extension)
 Scales / balance (for measuring the mass & mg
equation is used or for measuring weight) /
Newtonmeter (for the weight of hanging masses) / ‘known’ weights used

Determining Young modulus:
 stress = force/(cross-sectional) area and strain = extension/original length
 Young modulus = stress/strain / Young modulus is equal to the gradient from stress-strain graph (in the linear region)

Question 14

Describe how you could test whether the microwaves leaving the transmitter were plane polarised.

Answer 14

Place a metal grid {allow “Polaroid”} and rotate grid/transmitter/detector, this causes min/zero signal

Question 15

Explain how the stationary wave is formed on this string

Answer 15

the wave reflected (at the fixed end of the wire)

interferes/superposes with the incident wave to produce a resultant wave with nodes and antinodes/no energy transfer

Question 16

By considering the motion of progressive waves on the wire, explain how the stationary wave is produced.
In your answer you should make clear how the stationary wave arises.

Answer 16

the incident wave is reflected at the fixed ends of the wire
reflected wave interferes/superposes with the incident wave to produce a resultant wave with nodes and antinodes/no energy transfer

Question 17

Describe briefly an experiment to demonstrate the polarisation of microwaves in the laboratory.

Answer 17

place transmitter and receiver facing each other
rotate either transmitter or receiver through 90 degrees about axis joining aerials or use two polarising filters and rotate from parallel to crossed
observe signal fall to zero/minimum from initial high value on meter monitoring output of receiver

Question 18

Describe how you would demonstrate that a sound wave of wavelength 0.10 m emitted from a loudspeaker can be diffracted.

Answer 18

use a slit/hole/ barrier
width of gap/position beyond barrier comparable to
wavelength
microphone/observer’s ear suitably placed
sound detected/heard outside ‘geometrical shadow’ region (showing diffraction)

Question 19

The photons of red light are emitted by the neon atoms in the gas inside the laser.
Explain what energy levels are and how they can be used to explain the emission of photons from atoms.

Answer 19

energy levels explanation: electrons have discrete energies in atom
each photon produced by electron moving between levels
photon energy equal to energy difference between levels
electron loses energy/making transition in correct direction