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Monday, 24 February 2014

Assessed Homework

1.       (a)     friction;
attract;                                                                                                              4

  (b)   (i)      correct direction of movement shown (towards metal plates);                 1

(ii)     An explanation to include:
     ·  repelled from positive grid;
     ·  attracted to negative plates;                                                             2
[Allow like charges repel/unlike charges attract for 1 mark]

(iii)    to make dust particles fall off/
in order to collect dust particles/to clean the plates;                                 1



  2.     (a)     (i)      V across lamp;                                                                                        1

(ii)     A in series;                                                                                              1

(iii)    thermistor/variable resistor in series;                                                       1

  (b)   A calculation to include:

1. V = IR;

2. 12 = 1.6 × R;

3. R = 7.5;

4. Ohms;                                                                                                 4

  (c)   curve showing increasing R/decreasing gradient with voltage;;
starts at origin;
[Accept straight line through origin for two marks)                                          3



  3.     (a)     drag/resistance/force/push/thrust/upthrust;
[Reject wind/friction]                                                                                       2

(b)     56;                                                                                                                    1

  (c)    (i)      pull of Earth/weight/gravitational pull/downward (pull) greater than upward (push)/there is resultant force downwards;
[Allow gravity]                                                                                        1

(ii)     both forces the same/balanced/equal/resultant force is zero/OWTTE;     1

  (d)   (i)      speed decreases;
new lower terminal velocity/horizontal region shown;
(Independent marking points)                                                                 2

(ii)     An explanation to include three from:

·      air resistance increases;

·      at start upward force greater than downward force;

·      eventually forces balance;

·      larger surface area;

·      air resistance decreases as parachutist slows down;                            3



4.       (a)     (idea of) time for half of undecayed nuclei/atoms to decay
OR (idea of time) for activity/count rate halved;                                      1

(reject mass changes)

  (b)   1000÷2 [any other value (in range 500-1000)÷2];                                            2

(check graph)

          50 (47-53) (min);

(ignore unit)
(or alternative calculation for 2 marks)
[Reject 100/2 =50 for both marks]

  (c)    (i)      2 (Bq);                                                                                                     1

(ignore units)

(ii)     any two from:
contamination idea;

e.g. still waste there/soil contaminated

          opinion/perception of risk/worry/fright;
radioactivity can be harmful/dangerous/cause cancer/mutations;
2 Bq (or ecf from (c)(i)/only 2 half lives/remains radioactive for long time;           2



  5.     A



  6.     B