Enhancement Levels

Now I,m the first to admit I,m a bit of a dummy as to how things work in this game .
My question is if I have a level 50 character and slot everything at level 50,what happens to the enhancements if I say exemplar down to say level 25.
Do the enhancements work at level 25 strength or do the just stop working altogether,will apologize for the nooby question but I have wondered about this for a while now.Will say thanks for any enlightenment on this

It's actually pretty complicated. See this wiki page.

Basically, you can exemp down to level 32 with no change. Beyond that, your enhancements lose some of their value. The further down you exemp, the greater the reduction.

edit: oops, fixed link

StarGeek's answer is correct, but incomplete; it only covers the enhancement aspect of your enhancements. For sets, there's a little more to it.

Set bonuses are retained so long as you don't exemplar more than 3 levels below the levels of the enhancements. In your example with all level 50 enhancements, you could exemplar as low as level 47 and keep your set bonuses. Exemplar to 46 or lower and the set bonuses will all vanish.
If you mix the levels of the enhancements, they individually stop counting as you exemplar too low. For example, with 5 level 25 and one level 50, you would have all 6 set bonuses at levels 47-50, 5 pieces from level 22-46, and no set bonuses from 1-21.
The enhancement values scale down as per StarGeek's explanation.
Set pieces with special always-on bonuses (such as the Luck of the Gambler Global Recharge, or the Steadfast Protection Defense bonus) function just like set bonuses. You keep the bonus until you exemplar more that 3 levels below the enhancement. If it stops counting for set bonuses, it stops providing its special bonus too.
Pieces with procs (Chance for X) or use-activated bonuses (X bonus for 120s after using the power this enhancement is slotted in) will function at any level. Of course, since you have to activate the power they're slotted in to trigger them, if you exemplar low enough to lose the power they're in, you also lose access to the special enhancement.

Purple enhancements (including Catalyzed ATOs) and PVP IOs never lose their set bonuses or special effects when exemplaring; they remain all the way down to level 1. The enhancement values still scale down as StarGeek explained.

Attuned enhancements (Store Bought sets, ATOs, and the new set from the summer event) level up with you. When you exemplar, they are still treated as the same level as your REAL level, and then scale down to your exemplar level. Their set bonuses are retained at any level down to the minimum level for the set-3. So, if you have a set of attuned Luck of the Gambler (level 25-50), you keep the set bonuses and the Global Recharge boost all the way down to 22.

I'm pretty sure all of this is explained in the page StarGeek linked, but I thought I'd add it, just in case you're somewhere where that site might be blocked (ie, posting from work).

Ok as I thought it is a bit complicated seems its best to slot a mixture of lvls ,that way I will always have something there that is working.Thank you for your replies I understand it a little better now

I'm not sure I'd mix and match the levels. That would make your set bonuses rather difficult to predict which you'd keep when exemplaring.

Personally, I always slot Level 25s. I rarely exemplar low enough to lose those bonuses, and I'm still getting roughly the equivalent of SOs for enhancement values.
My goal is to keep all my set bonuses as close to all the time as possible. I only use a mix of levels when the set I'm using doesn't provide enough enhancement. For example, four Kinetic Combats has some incredible set bonuses, but the enhancement values aren't great, especially at level 25. I'll slot a couple level 50 triples or quads (usually Crushing Impact or Mako's Bite) to improve the slotting. For these latter ones, I don't care about the set bonuses at all.

Other people slot in the 30-35 range. This gives them noticeably better than SO enhancements, and they still rarely lose set bonuses. Note that somewhere in this range, boosting an enhancement to +5 makes it equivalent to a level 50 enhancement. Boosting an enhancement doesn't change its level, so it will still count as its base level with regards to set bonuses and exemplaring.

Correct. And the enhancement values will be close to those of level 50s (if not equal).

Note that it can be harder to find enhancements that aren't at the top of their level range. I tend to pay extra on the Auction House to get my level 25s, and I often have to use Merits to create the recipes I want, because the supply is low to non-existant.

Chiming in about exemplaring and levels of enhancements, level 41s give nearly the same value as level 50s even without enhancement boosters. They don't cost as much as level 50s to craft (though finding the recipes might be tough). You can use them exemplared down to level 38, which covers most of the content that is typically involved in Weekly Strike Forces.

Purple and PVP recipes/IOs are much more expensive than most regular IOs, but depending on what you are going for and how often you exemplar, they can be really nice. Most purple sets give +4% recovery, +15% accuracy, and +10% recharge (not all do, but those are really common bonuses). Compared to other non-purple sets that is good but not spectacular compared to the price . . . but if you exemplar a lot, you also have to factor in the bonuses sticking around. Many of the ATO sets are great too, and get even better if you catalyze them to make superior versions. They aren't as expensive as purples.

One not-so-obvious thing about exemplaring is how it affects enhancement value itself. As noted above, the enhancement value is the same down to level 32, then its reduced according to a formula. Individual enhancement values below 20% aren't affected until you his level 21. So if you have a level 25 dual IO that gives 20%/20%, or a level 43 triple IO that gives 19.9%/19.9%/19.9% the enhancement value won't get scaled down until level 21. That's not so shabby. Sometimes the set bonuses aren't as important as the enhancement value of the power itself.

Let me just add some more food for thought. When you exempt you keep any powers that you picked for 5 levels above what you exempted to. An example- a lvl 50 exempts to lvl 25, you still keep your lvl 26, 28 and 30 power picks. To keep the set bonus of that lvl 30 power when you are lvl 25 you would have to slot lvl 28 or lower IOs. So I will typically look for IOs that are 2 lvls lower than I picked the power to keep the set bonus when I exempt and still have the power available. Then boost the IOs if I feel the need to.