Questions asked by Sara

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• Could someone please explain to me what does it mean when an atom gets 'excited' and how they reach that state?
  
• Could someone please describe the shapes of electron density maps for s and p orbital? And why they're shaped the way they are?
  
• Why does the atomic radius of an element generally decrease across a period and why does it increase down a group?
  
• Why do nitrogen and phosphorus have high ionisation energies?
  
• Why does an increase in temperature cause a decrease in viscosity in liquids and an increase in viscosity in gases?
  
• Could someone please solve this?
  
• Can someone please explain this diagram to me? How do we know that the arrows are supposed to point upwards and not downwards? Why is O2 and C's arrow pointing to the pointing to the products side?
  
• What is the difference between hard, tough, strong and stiff materials? Can someone please give me definitions of these terms and examples of materials which show these properties?
  
• Could someone pls solve this bearings question?
  
• Could someone please tell me how did we get these values for bearings?
  
• Could someone pls tell me why did they substitute t = 3 hrs instead of t = 1500 hrs in part c)?
  
• Moments q. Could someone pls show me a better way to solve part c?
  
• Could someone please tell me better method to solve this using logs?
  
• How does this allow us to measure the potential difference across a diode?
  
• Projectiles q. How to solve part c) please?
  
• Help please?
  
• Could someone please explain (ii)* to me?
  
• How to solve this trig q? Help pls?
  
• Can someone pls show me the VR (Voltage-Resistance) Graphs for an NTC thermistor, filament lamp and conductors?