Half life

Markscheme for Homework on Static Electricity

1.       (a)     arrow drawn to the left;                                                                                    1

(b)     the sizes are equal;                                                                                           1

(c)     the strips have the same type of charge;
similar charges repel                                                                                         2

  (d)   (i)      electrons ;                                                                                                1

(ii)     positive, there are more positive charges than negative                           1

[6]

 

  2.     by movement of electrons/negative charge;                                                               2
from earth/switch to the man;
Reject positive electrons (for both marks)

[2]

 

  3.               any 2 from:
causal mechanism

Accept e.g.
(due to) friction/rubbing

Ignore repeat of stem

          what moves

Accept negative charge moves OR electrons

          which direction;;                                                                                               2

Accept onto hose OR from fuel

Reject incorrect physics

Reject for the last two marking points ions or positive electrons

          consequence AND some explanation;

both needed for the mark
e.g.
chance of explosion as fuel is flammable
chance of explosion/ignition if spark

Do not award repeat of stem… ‘it is dangerous’

Ignore (electric /static) shock

Reject unqualified explosion

          OR
explanation AND some consequence;                                                              1

Accept:
static build-up/it could ignite fuel
static build-up/it could cause explosion
spark/it could ignite fuel

          movement of charge (in wire);

Accept:
electrons/charges move (along the wire)
electrons/charges move (from hose to plane)

Reject ions or positive electrons for the first mark
UNLESS mark has been deducted in a

          effect of this movement;                                                                                  2

Accept:
this discharges it/the static build-up
this neutralises it
this earths it/to earth
this grounds it/to ground
gives plane and hose the same potential / same charge

Accept this prevents a build up of charge for both marks

Ignore floor

Mark in either order

 

QWC (1)

[6]

 

4) (a)      (i)     friction between the beads and pipe

accept beads rub against the pipe

1

(cause) electrons to transfer

accept electrons are lost/gained

do not accept negatively charged atoms for electrons

3^rd mark point only scores if 2nd mark scores

1

from the pipe

do not accept from the (negatively) charged pipe

or
to the beads

do not accept to the (positively) charged beads

accept negative charge transfer to the beads for 1 mark provided 2^nd or 3^rd marking point not awarded

mention of positive charge transfer negates last 2 marking points

1

(ii)     volume of beads

accept (75)cm³

or
length of pipe

accept use the same pipe

or

or
speed the beads are poured

poured the same way is insufficient

or
angle of pipe

1

(b)     (i)      the larger the beads the less charge

do not accept inversely proportional

negative correlation is insufficient

1

(ii)     (total) charge decrease

results would be lower/smaller would be insufficient

1

beads in contact with pipe (walls) for less time

accept less contact (between beads and pipe)

accept beads in pipe for less time

or
smaller surface area (to rub against)

accept less pipe to rub against

less friction is insufficient

1

(c)     (i)      (pumping very) fine powders

reason only scores if (very) fine powders given greater charge (build up)

accept more static (electricity)

accept an answer that correctly relates back to the experimental data

or
higher pd/voltage
or
greater energy

accept larger surface area to volume (ratio)

1

(ii)     idea of earthing (the pipe)

accept use metal pipes

do not accept use larger particles

1

(d)     to compare (the relative risks)

fair test is insufficient

you can only have one

independent variable is insufficient

or
different conditions change the MIE value

accept different conditions change the results

do not accept avoid bias

1

 

 

  (a)     (i)      Ends have charge
Which is opposite on each rods

 

(ii)     Attracts

 

(b)     (i)      Repulsion

 

(ii)     Ends have same charge

 

(c)     Electrons move between cloth and rod
Where gather is negative
Where move from is positive

3

(6 marks)