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Marks 4 U - Prefixes

Marks 4 U - Prefixes. kg (kilogram) is the only SI unit that has a prefix - all the others don’t i.e. A (ampere) J (joule) m (metre) N (newton) s (second) V (volt) W (watt) Ω (ohm). These are the “tricky” ones.

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Marks 4 U - Prefixes

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  1. Marks 4 U - Prefixes kg (kilogram) is the only SI unit that has a prefix - all the others don’t i.e. A (ampere) J (joule) m (metre) N (newton) s (second) V (volt) W (watt) Ω (ohm) These are the “tricky” ones If your quantity (number) has a prefix then you multiply the number part by the value of the prefix to get units. Example: 120kJ = 120 x 103 = 120,000 J Example: 350 mm = 350 x 10-3 = 0.35 m If you have a number and you would like to use a prefix then you divide the number by the value of the prefix to get the Number with a Prefix Example: 0.35m = 0.35 ÷ 10-3 = 350mm Example: 120,000J = 120,000 ÷ 103 = 120kJ

  2. 2 3 4 Marks 4 U - momentum 1 Use “u” for velocity before and use “v” for velocity after collision Divide you page down the middle and label Before and After (collision). Draw a diagram! Before = After Write down your formulas Substitute values: Remember to look for stationary objects - their velocity is zero and that part of the equation goes away! Now let LHS (before) = RHS (after) Then solve for unknown value (i.e. what the question asked you to find) Note : the unit of momentum is kgm/s or kgms-1 Note : the formula for momentum is given as p=mv in the Data Booklet

  3. 2 3 4 Draw diagram or sketch List known and unknown quantities Draw line down centre of page Marks 4 U - Projectiles 1 Constant Acceleration due to gravity Constant Velocity … (Newton’s 1st Law) On LHS write Horizontal On RHS write Vertical Constant Acceleration Constant Velocity Time (t) is common to both horizontal and vertical motion

  4. Marks 4 – Speed/time graphs Speed or Velocity (ms-1) constant speed deceleration constant speed acceleration deceleration Distance travelled = Area under graph time (s) NOTE: v > u gives acceleration; v < u gives deceleration or negative acceleration

  5. 2 Marks 4U : Voltage Dividers 1 Before you begin. Remember that VS= V1 + V2 Now write down what you know and don’t know ! There are two formulas associated with Voltage Dividers Try to use formula 1 first. You need 3 of the 4 terms V1, V2, R1 or R2. (VS is not required) R1 V1 Vs R2 V2 Use this formula if you can’t use formula 1. Look for VS in the question. Again, remember that VS= V1 + V2 … you don’t need to use formula 2 twice!

  6. 2 Marks 4 U - Transistor 1 The question will indicate whether the temperature (Thermistor) or light (LDR) is increasing or decreasing. Use this information to start your answer e.g“As the light level falls the resistance of the LDR increases …” This could be any output device, e.g. relay, bell, buzzer etc. 3 Explain the Science of the LDR (L.U.R.D.) or Thermistor (T.U.R.D.) LDR1 The LDR or Thermistor may be placed here – you need to think how this affects step 2 Vs Explain How the Transistor works:- Switches ON at the threshold voltage 0.7 V for npn transistor 1.0 – 2.0 volts for MOSFET V2 R2

  7. 2 Marks 4 U - Transformers 1 Read the question carefully and select two of the three terms (ratios) shown in the formula – you should end up with a simpler relationship containing two terms (ratios). Copy this from the Physics data booklet 3 4 • Transformers are not 100% efficient due to • Heat loss • Magnetising currents • Sound (vibrations) Cross multiply to simplify then solve for the unknown term..

  8. 2 Marks 4 U - Heat 1 Temperature(T) Gas 3b 3a Cooling Curve Liquid Solid When material is cooling it gives off heat energy When its temperature is increasing the material is absorbing heat energy time(t)

  9. Marks 4 U - LED 1 2 3 4 5 LED numerical questions are usually worth three marks. The question usually gives the operational or working voltage of the LED … and the operational or operating current of the LED. Then it asks you to calculate R The current through R is the same as the operating current of the LED This is where you get the extra mark R Vs Remember to include unit Ω

  10. Marks 4 U – Half life 1 3 4 2 If the question asks you to find a “half life” or “how long a sample takes to decay” or “the initial or final level of Activity” then it’s a good bet that you need a ………….. Tablewhere you fill in the Blanks Fill in the initial Activity Divide previous Activity by 2 Divide previous Activity by 2 Until you reach your Final Activity Activity (units) Time (units) 0 Initial time = 0 Add one ½ Life to previous time Add one ½ Life to previous time Until your reach your Final time You will get the Units from the question To find the number of half lives – count the number of entries you have Made in the time row, but don’t count the first one (the zero value). To find the Half Life divide the final time by the number of half lives

  11. Marks4U – pulse generator 1 2 3 4 ½ mark Initially Vc = Logic 0 (0V) R1 Not gates inverts Logic to Logic 1 (5v) This is applied to top of R1 Capacitor charge up to Logic 1 (5v) ½ mark Not gates inverts Logic to Logic 0 (0v) This is applied to top of R1 Capacitor discharges to Logic 0 (0v) Logic 0 = 0V Logic 1 = 5V Timing/ Frequency determined by R1 and C ½ mark The process repeats ½ mark

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